FAQ:
How does the 4th pole switching reduce harmonic voltages?
Should I choose Single Phase 1 or 2 Pole?
How do I rate my STS requirement?
Protection and Discrimination how to, what kA capacity?
How do I determine the Type Number of the STS you require?
What are the configuration considerations?
Why are there fuses in Model B Static Transfer Switches and not others?
Should I choose centralized or de-centralized STS implementations?
What Monitoring & Control Options are available?
What is SCR / Thyristor Short circuit and Open circuit Detection?
Can I use RCD's or ELB's with a rack mount static switch?
Can I request a special design?
Can I get a Front Panel Emergency Power off on our STSs?
Is it OK to leave the back feed test switch in the test position after installing within the rack?
Can we get backfeed protection without causing our Earth Leakage Breakers to trip, (ELCB)?
What do we specify when we want the mechanical disconnect option fitted?
3 or 4 pole ?
If your distribution doesn’t employ an MEN system for interconnected continuity of Neutral to Earth potential bonding or you employ Neutral Isolation (e.g. 4-Pole Isolation / Protection CB’s and alike) then you may need a 4- Pole STS.
Similarly if you have a 3 wire distribution system then you will not get a benefit from a 4-Pole STS so use a 3-Pole.
If the MEN point of the two feeds are some distance apart from the STS / Load or the sources are a long way apart of are from differing sources it is usually necessary to switch the neutral to steer the neutral currents back to their source via the shortest path rather than letting them find their own rout which will normally be longer. Steering the neutral currents with the phase currents will significantly reduce the harmonic voltage distortion for the load; especially when the current paths are quite long and / or there is significant current distortion.
Now if the above doesn’t apply or if you have multiple MEN or neutral bonding points within your distribution and the cable lengths are short then a 3-pole will most probably be OK.
How does the 4th pole switching reduce harmonic voltages ?
Conductors like copper cables are not perfect conductors of electricity and they have some loss when carrying the currents. They have a DC resistance or volt drop. Similarly for AC currents there is an additional Impedance drop (inductive) caused by the fields produced by the currents flowing. If the cables are well grouped (e.g. R, W, B & N in a tight trefoil configuration) then this inductive impedance is reduced because the fields cancel reducing the effective inductance. Once separated the field no longer effectively cancel. Impedance drops are inevitably several orders larger than the resistive drops and contribute to the end voltage at the point of usage especially if the cable runs are long. The larger the current harmonics caused by the load the greater the voltage distortion caused by the series impedance introduced by the separation of currents. Hence by switching the neutral as w3ell as the active conductors (e.g. 4-pole), it is possible to steer the currents back to their sources and adjacent phase conductors and reduce the impedance resulting in better voltages at your load.
Don’t you generate dangerous voltages when you break the Neutral in a 4-Pole STS.
i-STS standard main phase conductors are break before make (Break is not seen by the load as it is very short but necessary to ensure that the phases of different sources are not paralleled. The Neutral however, is make before break (overlapping) and stays on until all of the currents in the previous conducting phases have ceased (+ approx. 15 msec). This ensures that dangerous voltages are not generated by the breaking of the neutral.
Single Phase 1 or 2 Pole ?
The criteria for single phase STSs necessity for 1 or 2 poles is similar to the 3 vs 4 pole scenario associated with current steering and cable impedance reductions. For single phase the neutrals do not overlap as there is only one active current path and one neutral return.
Also as these are usually installed near the load “Point of Distribution or usage” in IT racks typically and usually an important consideration is to ensure that the neutral conductors are not inadvertently overloaded as a result of stray neutral current paths from other loads (which could cause neutral overloading within the site).
How do I rate my STS requirement ?
Choosing a rating should be easy and can be determined by summing your equipment current demands. STSs are rated by their maximum RMS phase current not generally by kVA and KW.
It is important to rate the STS for the maximum phase current plus any future growth estimates. If in doubt we can undertake an audit (measurement). This measurement should be undertaken during normal operation and certainty is improved by continuous logging over 24 Hrs/ 7 days / Month etc. This is especially if you have times of varying demands associated with your business operations. It is important to also measure and monitor your load neutral currents as often these sum to a higher value than the phase currents which would / could otherwise cause neutral current cable overloading.
In addition to the current demand you will need to specify the3 nominal voltage and frequency and any significant specific electrical variations (e.g. must operate from generator with a freq variation of X, or a Voltage variation of Y or a THD(V) of Z etc).
It is always wise to explain any abnormalities although these may often have no aff4ect on the implementation they are best considered, (e.g. STS sis supplied by 2 UPSs of similar rating, however, if they are from different manufacturers or different topology or different rating or performance it may be prudent to alter the STS operating parameters to provide better protection for then load and the sources,, (e.g. some older UPSs were not made to accommodate a 100% step change in loading as may be likely when transferring the full load from one UPS system to the other). Similarly the STSs may have sources from non UPS sources (from mains, and generator or essential and non essential supplies which could be affected / degraded by other non critical equipment loadings, e.g. lifts, high V distortion, sags and surges making it a non preferred source.
Remember that an increase in the neutral current capacity (e.g. greater than the phase currents) usually results in over sizing of the STS as a whole when a 4-pole STS is under consideration. This is because the 4th pole in any series isolator or maintenance bypass facility is rated the same as the phase conductors current ratings. Hence if you ask for a 4-pole, 250 Ampere STS with 2 X Neutral rating the isolators will need to be rated for 500 Amperes. The same is not true for an STS with a common neutral as the neutral with the STS is only used for referencing purposes rather the main currents.
Protection and Discrimination HOWTO ? what kA capacity ?
i-STS STSs have generously overrated power components and may not incorporate fuses or current limiting circuit breakers (except rack mount or < 63 Amperes). In larger units we’ve found that it makes for simpler discrimination when it comes to downstream or load faults if the STS plays no role in the protection scheme and leave this to the down stream and up stream devices. To achieve this successfully all you need to do is set the upstream (sources) MCB/ACB to limit the maximum let through current to the capacity of the STS. (e.g. generally 16 or 35 kA for 10 msec up to 65 kA). Normally this is just a case of setting the dial on the circuit breaker to the setting recommended by the manufacturers circuit breaker tripping curves. You may need to know your maximum source fault current, the length and size of cable between eh source and the STS. Then by simple calculation and a look up table / chart the setting is attained and set on your circuit breaker. If you need help ask us or your consultant to help as we understand that this may not be your domain / expertise.
So i-STSs come 2kA (for B & B1 & B3 point of distribution rack mount (still OK for up to 20kA but may blow fuse or device iof fault current is greater than 2KA), (10 – 63 Amperes)
16kA (10 msec) for Model C and Model H Static Transfer Switches, (40 – 250 Amperes)
35kA (10 msec) for Model M & G Static Transfer Switches, (63 – 1250 Amperes)
50 kA (10 msec) for Model G & L Static Transfer Switches, (600 – 1250 Amperes)
65 kA (10 msec) for Static Transfer Switches, (1500 – 3000 Amperes) or when a number of lower fault current cycles needs to be tolerated.
How to determine the Type Number of the STS you require ?
i-STSAAA/H/3P4-415/50 where AAA is the current rating
H represents the physical attribute (for Model H or Mode M)
3p4 represents the number of phases and poles respectively
415/50 the nominal voltage and frequency respectively
Configuration Considerations
Once before we became reliant on computers we could afford a couple of flickers in the supply; but as time progressed and it became more inconvenient and costly to cope with these interruptions we found we needed a UPS. Today more than ever our businesses are more reliant and our customers expectations require a 24/7 99.9XX reliability or availability. This is not achievable using a UPS alone. Because a UPS is quite complicated with significant active power switching devices incorporating electrolytic capacitors, batteries and even air-conditioning plant the UPS alone (with MTBF of 100,000 Hrs typical) can only provide a 92% confidence level (e.g. statistics show a greater than 8% chance of failure within a year).
There are many configurations that endeavour to improve this confidence level:
Things to consider:
- Does the customer have dual cord power supplies implementations within their loads (e.g. equipments with more than one power supply, 2 x AC inputs), ; if one AC source should fail then the equipment will continue to operate from the remaining source.
- What proportion of dual cord vs single cord (measure single cord loadings)
- Some equipment is tri-cord in that it needs 2 of the three sources to be available to operate correctly.
- It should be understood that dual cord equipments may draw power from either input or both
Why are there fuses in Model B Static Transfer Switches and not others?
Our static switches are manufactured to be rugged and our larger units don't have internal protective fuses and or circuit breakers. The devices are purposely overrated to cope with external short circuits without failure or loss of output.
For safety reasons there needs to be some protection between the source and the load. This protection is graded to limit the fault currents to below the specified fault rating (kA rating) such that the protective device opens the circuit within 10 milliseconds, (1/2 a cycle). Most circuit breakers will enable settings to be selected to easily achieve this.
kA Rating of devices vary from 2kA in small Point of Distribution Rack Mounted Static Transfer Switches to 9kA, 15kA, 30kA, 36kA, 40kA and 50kA and beyond. This additional kA capacity is gained by over sizing the semiconductors used to undertake the switching process. Obviously the higher the kA rating the larger the device and the greater the cost.
If you choose to low a kA rating or do not have the correct upstream protection settings the devices could fail. Although failure does not cause loss of output the STS will no longer be capable of transferring the critical load to the alternate supply source.
Model B, B1 - Point of Distribution Rack Mounted Static transfer Switches, (1U and 3U)
These units incorporate the latest power modules, (100 / 120 Ampere continuously rated devices ) to provide absolute ruggedness in a small conveniently locatable enclosure for improved margins and a no worry load fault / inrush capability.
These models contain fuses. The fuses are for final STS protection only. We would expect that the down stream fuses in the faulty equipment will always clear first. Thus loss of output due to internal STS failure is not likely to occur except for the most arduous operating conditions. Below you will find their capability.
The units contain fuses that ensure safe installation for supply capacities up to 20 kA.
§ Allows for installations with extremely high fault current capability (up to 20 kA)
§ Up to 100 Amperes for in excess of 30 seconds and 200 Amperes for 25 cycles, (1/2 second).
§ Overload and fault withstand capacities of at least 2000% (400A) for 100msec without rupture of internal 100A fuse and without damage to the STS semiconductors.
§ Fault Current characteristics where fault current is in excess of 2000 Amperes the internal 100A fuse will rupture safely and the STS semiconductors will not be damaged.
§ At fault current between 2kA and 20kA, the internal 100A fuse will rupture safely and the STS semiconductors will fail safely.
In practice down stream equipments contain small fuses where discrimination ensures that they clear first. The fault current values indicated above are seldom found in rack mounted arrangements as the cables interconnecting the source and the load limit the fault currents to very low values below what would cause the fuse to isolate.
Centralized or de-centralized STS implementations ?
e.g. either
1 Large STS as part of the distribution system (such as Model M & G)
2 Small STS at Point of Distribution / use (Inside the IT 19 Inch equipment racks, (suits Models B, B1 & B3)
3 UPSs are on a different floor than the load and distribution of power is via sub boards on different levels / floors (suits Model H and Model C)
In any case it is best to locate the STSs as close to the critical loads as possible. However, this does require dual feed distribution from the UPSs to near the point of distribution for this to be possible).
Then for the safest system we have
Redundant parallel operated UPS configurations which alone also flounder in their attempt to increase reliability estimations marginally above 200,000 Hrs. A far cry from the 1,500,000 Hrs that these configurations derive from theoretical calculation.
This inability to achieve theoretical values is usually because of equipment and distribution interdependences. i.e. They are not truly independent and a failure of one item tends to cause failure of the system as a whole.
Dual and tri - chord distribution systems were developed to remove these interdependences, however, not all computer room equipment has dual / tri chord technology implementations and occasionally for those that do; the systems often cannot survive with one source removed.
Static Transfer Switches, (STS) provide a convenient and effective way of addressing the loss of a supply by transferring the critical load to an alternate power source. A good switch will do this transparently to the load irrespective of the nature of the degradation or fault on the supply side. As long as there is a healthy supply the STS will maintain critical power to your systems.
Because STSs are not as complex as UPS equipments, operate independently and are close to the point of power usage reliabilities of 1,500,000 Hrs are realizable. That’s an availability of 99.4% or 0.65% chance of unavailability.
There are basically two schemes to consider. Centralized and de-centralized distribution.
In the centralized system large capacity Static Transfer Switches take the power from two UPSs and a single feed is distributed to the critical loads which may be on different floors within a multi story building. Sometimes two UPSs and 2 Static Transfer Switches are employed to deliver 2 feeders throughout the building thus improving additional security dual cord distribution.
The Key features to a centralized critical power distribution scheme are outlined below:
To dual equipment with dual cord power supplies
In these larger distribution systems single cord equipment is also supplied but not protected against distribution / switching failures down stream of the equipments. These equipments are typically rated from 100 – 1250 Amperes and need to be capable of withstanding large fault currents because they are usually placed in, near or adjacent to the electrical power reticulation infrastructure.
Other schemes distribute the main feeders of the two UPSs up the building close to the critical loads and then use Point of Distribution Static Transfer Switches in 19 inch rack systems to supply critical non dual cord equipment power. This provides the single cord equipment with almost the same reliability as the dual cord equipment topology, (see diagram overleaf).
In a de-centralized (Point of Distribution system) the critical loads are protected right up to the critical piece of equipment. The Equipment is much smaller in rating because the power density in the rack is limited but typically these Static Transfer Switches are rated from 10 – 63 Amperes and can be either single phase single or double pole or three phase 3 or 4 pole. Because the Static Transfer Switches are so efficient (99.8%) there is almost no heat contribution, take up only 1 RU (44mm) of space and generally provide greater overall system reliability because you’re not putting all your eggs in one basket, (e.g. can build in redundant operating systems and load distributions so that a failure of one aspect of the distribution system doesn’t cause failure of the mission critical IT infrastructure as a whole.
De-Centralized –Point of Distribution System
The larger centralized schemes generally and mostly always employ Thyristor or SCR based Static Transfer Switches. These are very reliable and very rugged.
In smaller de-centralized systems or point of distribution type utilizations sometimes non static (thyristor or SCR) based switches are used because they are cheaper. These often utilize fast switching electromechanical switching devices. These have breaks in excess of ¼ of a cycle, sometimes approaching a whole cycle under loss or low supply conditions. Much equipment may ride though this period, however, some won’t and the more expensive and critical the equipment becomes the more critical to short power interruptions it appears to be.
Further if a load fault occurs the STS must not transfer the fault to the alternative source and must be cleared by the original source.
So what is the alternative technology?
1RU Static Point of Distribution Transfer Switches are available and address all of the shortfalls of their electromechanical counterparts. To achieve effective no-break supply transfers solid state switches are necessary. Typically these contain thyristors which are robust and have a very high load fault tolerance.
These are found to be suitable but for the most critical of equipments. The only disadvantage of thyristor only STSs is that they switch over at current zero not at the point in the power cycle where a transfer is initiated. Under certain conditions it is not uncommon for these STSs to have a break well in excess of around ¼ of a cycle.
A new class of active switching point of distribution Static Transfer Switches is now available. These incorporate an active switching device which is able to statically interrupt the load current and affect a supply change-over anywhere in the power cycle and in less than 1/10th of a cycle. Because these switching devices have limited fault clearing capacities additional bypass thyristor is used to let through critical load fault currents if and when they occur. These incorporate a fuseless design and also allow installations up to 20 kA (10 msec), and are now available in capacities from 20 -> 120 Amperes in all configurations, including single or three phase 1, 2, 3 or 4 pole all within your standard 19 inch rack enclosure.
What Monitoring & Control Options are available ?
Monitor via pre-defined voltage free relay contacts…
All output relays contacts are rated for 50 V DC 1 Ampere (Not 240 V AC rated)
User Remote Inputs (Voltage free contact closure controllers only)
COMM -> Common return
a -> Transfer to Supply 1
b -> Transfer to Supply 2
c -> Fire Stop (Causes both Switches to go off – loss of output OPTIONALLY DISABLED)
User Relay Outputs
Relays are normally closed and held open in OK state (closed contact represents the alarm state).
A -> General Alarm
B -> Not in Synchronism
C -> Supply 1 OK (Not avail on B1)
D -> Supply 2 OK (Not avail on B1)
E -> ON Supply 1
F -> On Supply 2
G -> Overloaded
RS232 PORT (The RS232 port provides MODBUS RTU via RS232. The port does not provide for electrical isolation. Refer to the Static Power Modbus Interface Specification for information about accessing information through this port. MODBUS via RS422 or RS485 multi-drop is available with hardware third party adapter. This allows all variables, status, alarms and event histories to be extracted. Also enables STS control of Transfer to S1 and Transfer to S2.
Printer Port (available soon)
LAN
The LAN interface provides a internet browser interface that allows access to all settings.
Optional
Modbus TCP
SNMP (uses modified UPS MIB)
All settings are user accessible via password via either LCD or LAN (except load fault)
There is no proprietary software that is required to access or display any of the system information.
SCR / Thyristor Short circuit and Open circuit Detection
All i-STS Static Transfer Switches incorporate SCR/ Thyristor Short Circuit and Open Circuit conditions. In each case when detected the load is protected and further transfers are inhibited until the condition has been addressed.
Rack mount STSs Detection of open circuit and short circuit is undertaken by opto-couplers that are connected between the incoming supplies and the output. When gating is removed within less than a cycle the Thyristor should extinguish and voltage will build up across the switch. If this occurs the Thyristor is not short circuit.
Once the OK condition has been detected, (the Thyristor is off), the alternate supply Thyristor is gated on. If the previously non active supply Thyristor fails to come on (as detected by the voltage still being across the opto couplers) then this is detected as an open circuit.
s/c condition on active side-> at transfer manual or auto transfer operation. If detected immediate re-transfer to existing selected supply if un-successful and further transfers are inhibited. The event history reports the finding. If successful normal operation continues.
s/c condition on inactive side -> during any manual or auto transfer operation. If detected immediate a transfer to the previously inactive side is undertaken and further transfers are inhibited. The condition is reported in the event history.
Back feed protection -> within 5 seconds after removal from the source a safety circuit shunts the leakage current to ground. The resulting residual AC voltage on them bare plug must be less than 30 V RMS or 42 V peak.
o/c on active side – Transient low condition indicates that Thyristors open circuit. Also during any manual or auto transfer operation This results in an immediate transfer to the previously inactive side and further transfers are inhibited. The condition is reported in the event history.
o/c in inactive side – This is detected during any manual or auto transfer operation. When detected a transfer to the inactive side is prohibited. The condition is reported in the event history.
Large Free Standing STSs (with Incoming STS Isolators)
s/c condition on active side-> at transfer manual or auto transfer operation. If detected immediate re-transfer to existing selected supply if un-successful. The isolator on the inactive side is shunt tripped. The event history reports the finding. If successful normal operation continues.
s/c condition on inactive side -> is detected by measurement of phase currents in non conducting side also during any manual or auto transfer operation. If detected immediate a transfer to the previously inactive side is undertaken and the previously active side isolator is tripped. The condition is reported in the event history.
Back feed protection -> within 10 seconds after mains failure is detected a check of AC volts on failed supply is undertaken (must be less than 30 V RMS or 42 V peak). If a voltage is apparent on any phase at any time during this mains failure period the isolator on the incoming failed supply is tripped. The condition is reported in the event history.
o/c on active side – Transient low condition indicates that Thyristors open circuit. Also during any manual or auto transfer operation This results in an immediate transfer to the previously inactive side. . If detected immediate transfer to the previously inactive side is undertaken and the previously active side isolator is tripped. The condition is reported in the event history.
o/c in inactive side – This is detected at transfers periodically during any manual or auto transfer operation. When detected a transfer to the inactive side is prohibited and the isolator of the inactive faulted side is tripped. The condition is reported in the event history.
Neutral open circuit and short circuit isolator tripping conditions operate as described above.
Use of RCDs or ELBs on Rack Mount Static Transfer Switches
Thyristors / SCRs are not perfect switches in that small leakage currents in the mA range can be experienced when the device is not conducting.
This equipment is not recommended to be installed where RCD associated with shock protection of personnel on the incoming sources is installed (e.g. instantaneous trip @ < 30 mA). Although the reverse leakage current of thyristors / SCRs is usually low (< 10 mA), many RCDs are set to operate around this level and installation in such an environment could lead to unreliable operation.
The following CAUTION applies:
The following Warning note applies:
This is especially important when plugging and unplugging the input (supply 1 or supply 2) plugs as leakage currents could cause dangerous voltages to appear on the incoming leads which can be a shock hazard and cause equipment damage if contact with personnel or other equipment is inadvertently made.
A safety circuit has been installed to shunt these leakage currents to ground when the incoming source lead is disconnected to ensure that the voltage at the bare plug end remains below 30 V AC, however, treat as live in cas the device has failed and full voltage appears at the plug ends,
It is possible to test in an RCD environment by temporarily switching the red slide switch on the LS of the unit to the back of the unit.
TREAT ALL UNPLUGGED LEADS AS LIVE
Relay based Point of Distribution STSs vs SCR/ solid state
In general relay based transfer switches suffer from the following:
· They use voltage sensing only and if there is a load fault they transfer the fault to the other source
· They look only for voltage failures and therefore can still send bad power to the load
· They can transfer out of synchronism
· Relays & contact ratings are very small and there have been many instances of contacts that have welded together or blown open circuit.
· Their break times are 12-25 msec
· They have no lock out so can continually transfer between the sources until they break
· They have no smarts to allow for HLI monitoring or user settings
They are advantageous for installations associated with RCDs or ELCBs connected to the incoming sources as an open relay contact
Ours use thyristors and transfer at zero current crossover.
The transfer time is typically < 1 msec but under worst case conditions can be up to 5msec (1/4 cycle)
· Our unit have generous overrated components utilize 100 Ampere devices / 1700 volts and 100 Ampere internal fuses.
Therefore have generous overload and fault capability
· Our units are suitable for and safe for installation into 20 kA distribution systems.
· Easy to see LED & backlit LCD & LAN Server built in (for Brower) & Modbus all built in.
· Everything is settable by the user if required (password protected)
· Redundant voltage sensing of all inputs and outputs for both steady state and transient levels
· Triple redundant power supplies
· Up to 32 Amperes, Naturally air cooled
· Your choice of input output connections
· Will not transfer a load fault
· Will not disconnect the load even under fault conditions (only uses upstream protection)
· Thyristor /SCR open and short circuit protection
· Real time event recording via LCD including Variables, history, settings and status
· Independent internal controls for HMI and also LAN and control algorithm in Hardware (integrated into CPLD)
· Preferred source selection, controls override (Auto / Manual Switch)/audible, visual alarm and much more.
· All surface mount technology (no transformers inside)
· Power components all double bonded soldered.
· 2 Year warranty
Because we locally manufacture these we have some scope for customisation in respect to inlet and outlet types,
e.g. your client may prefer Clipsal series 56 outlet plugs or IEC 309 or IEC 320 C20 inlets on 3 metre leads (2 meter leads are standard). OR you may wish to have the outlets not as 8 x C13 but on umbilical chords with IEC C19 outlets to supply you PDUs directly etc.
Please feel free to discuss your clients specific requirements if they are not met by our standard product, (POA).
We also manufacture Static Transfer Switches of much higher ratings to 2,500 Amperes so we definitely have the experience and know-how.
Most of our implementations have come directly as a result of customer requests to meet certain performance and physical attributes.
The Model B1 was designed specifically to replace the inferior relay type units,
Model M were made to fit into corridors and Model Cs were for wall mounting where there often isn’t any alternative.
We make STSs with larger capacities in smaller frame sizes than any other manufacturer.
If you have special physical requirements let us know , because we manufacture locally we are easily able to adapt the physical attributes to meet your application.
The STS can be colour coded to meet your adjacent equipment colour scheme otherwise RAL7035 is our preferred colour for large STSs and matt black for Rack Mount units.
Can I get a Front Panel Emergency Power off on our STSs?
Larger STSs and the Model B/B3 STS has incoming isolators that can be easily turned off and on.
For the Model B1we have two options.
1.
A front mounted (shrouded) latching pushbutton will, when pressed, remove gating from both sources, causing power to be lost on the output of the STS.
2.
A front mounted (shrouded) latching pushbutton, when pressed, disconnects power to the STS. It uses a relay/ contactor to disconnect both the active and the neutral from Source 1 and Source 2. This provides mechanical isolation as opposed to electronic disconnect as above. Obviously you’ll lose the output when both inputs are disconnected. Instead of a latching pushbutton the EPO can also be provided using a selector switch. POA.
Is it OK to leave the back feed test switch in the test position after installing within the rack?
The purpose of back feed protection (which you must not leave disabled) is to is to protect the user from electric shock when they unplug an input lead from its source socket. Normally, an unconnected input plug will have a voltage appear across it when the other input plug is connected. This is because the solid state devices used in the STS are not perfect switches and let through some leakage current, which creates a voltage across the terminals. The back feed protection circuit eliminates this danger by shunting any leakage current to ground, there-by ensuring that the residual voltage on the plug is at a safe level if inadvertent contact is made. If you have an issue with ELCBs (Earth leakage detection breakers) in your distribution system tripping, then we would recommend the following:
Can we get backfeed protection without causing our Earth Leakage Breakers to trip, (ELCB)?
Your Model B1 can have a relay/ contactor fitted to the incoming sources (inside the STS) so that when a supply failure on Source S1 occurs the contactor will physically disconnect supply Source 1 so that no backfeed from Source 2 can appear at the terminals of Source 1. The contactor never actually breaks or makes current because the STS portion is so quick that it transfers the critical load to the alternate source (in this case S2) if it was previously on S1 (or visa versa).
What do we specify when we want the mechanical disconnect option fitted?
Specify you STS with a suffix “I”, e.g for a 25 Ampere STS with standard voltages you would specify a “i-STSB125s1P2-230/50I” (The I is at the end of the normal part number.
Similarly if you need the Emergency Power Off option (EPO) the part number has a suffix EPOI for the mechanically isolated version (e.g. “i-STSB125s1P2-230/50EPOI”) OR “i-STSB125s1P2-230/50EPO” for the electronic disconnect approach.
I want to use your STSs in a number of locations. Some are 50Hz and some 60Hz, some are 100V AC and some are 240 V AC. Do I need a different type of unit for each application?
Normally units are supplied with fixed, pre-defined nominal voltage and frequency settings. Units can be factory calibrated before shipment for any voltage and frequency.
However, units can be provided with universal voltage and frequency tolerances which may be installed anywhere. These units will determine the correct operating frequency and voltage at start-up. The standard / nominal operating voltages are 220/110 ± 20% and 50 & 60 Hz ± 10%. If you have requirements for other nominal voltages it may be appropriate to set the lower or upper tolerance limits to compensate. This method is limited to 264-85 V AC due to operating requirements of internal components. POA.
We are interested in your three phase rack mount STS but haven’t got the room in our racks. What alternatives are there?
Please consider our NEW Model B2. It’s just 2RU high, (88mm) and 400 mm deep. It truly is the smallest three phase STS on the market. Substantial space and cost savings have realized by the use of new power semiconductor technology and SMT machine assembly. It’s available in ratings from 10 Amperes to 63 Amperes and suitable for installations with various nominal voltage and frequency (e.g. 50Hz or 60Hz, 440 – 200 Volts) and fault capacities of up to 20kA