ATS Panel Wiring Diagram Pdf
There are two basic configurations: CONTACTOR-based and CHANGEOVER-based. We analyze all aspects and clarify all the Pros and Cons.
ATS CONTROLLER INSTALLATION MANUAL
PROTECTION CIRCUIT BREAKERS
The controller senses the MAINS and GENERATOR voltages via a direct connection. You also have to provide power to the contactor coils. It is quite dangerous to connect these parts to high-power sources. The MAINS and the GENERATOR can supply hundreds of amperes in case of a short circuit. The wires may burn completely. Not to mention the risk of injury and fire. Circuit breakers that limit dangerous currents to the internal auxiliary circuits are mandatory. We consider that 10 Amps are more than enough for this application. Use wires with a minimum size of 1.5 square mm. Using circuit breakers simplifies troubleshooting.
The AMCB and AGCB prevent damages against internal short circuits.
THE BREAK-BEFOR-MAKE CONCEPT
In case of mains failure, there is no voltage in the load. Big electric motors stop to rotate in a few seconds. It will take seconds, but also minutes, to get power from the generator. After this delay, the back-EMF will not be dangerous. The KG can close safely. Unfortunately, depending on the settings, when the mains are stable, the transfer switch is theoretically capable of removing the generator and connecting the MAINS, This could be a problem in case the load features an inductive component. For this reason, the ATS controller features a “dead time” of about 2 seconds. This ensures a safe MAINS connection because there is no voltage on the load (due to the back-EMF phenomenon).
THE ENGINE CONNECTIONS
The ATS controller features a universal multi-functional interface board. This will allow you to connect all kinds of engines. It is possible to connect a simple engine that features a key start.
You can also connect engines that include their auto-start module. The relay output terminals 2-3-4-5 and 6 feature the necessary set of commands to start and stop the engine. It is a good practice to insert pilot relays on the engine frame. The outputs are circuit-proof. We recommend to limit the total output current to 1A. The ATS controller features 2-input and 2-output configurable terminals. The connections are through removable female connectors. Once you put the interface board on the panel, the user may directly connect the auxiliary circuits for the engine.
ATS PANEL WIRING EXPLANATION
We describe the status of the ATS panel when the LOAD is connected to the MAINS and when the LOAD is connected to the GENERATOR. In this example, we illustrate a CONTACTOR-BASED changeover, the MOTORIZED TRANSFER WITCH shares the same logic.
ATS PANEL: MAINS-LOAD
The four-pole MC contactor connects the LOAD to the MAINS. The four-pole MC coil energizes via the KM output and the AUX-G contacts.
The COIL of the four-pole MC is then supplied via the Neutral and phase T of the MAINS. When the ATS controller detects a MAINS failure, the ATS controller opens the KM output. The four-pole MC disconnects the LOAD.
ATS PANEL: GENERATOR-LOAD
When the ATS controller activates the output KG, the coil of the four-pole GC energizes. The LOAD is connected to the GENERATOR. The four-pole GC coil is energized via the normally closed contact on the body of the four-pole MC contactor.
In other words, the four-pole GC can energize only when the four-pole MC is open. The Neutral and phase L3 supply the coil of the GC. When switching the GENERATOR to MAINS, the user observes a short ‘power outage’. This is normally 2 seconds. This is the typical behaviour of the ATS based on contactors: BREAK-BEFORE-MAKE. A mechanical interlock on the 4-pole MC and GC provides additional safety.
ATS PANEL PROTECTION
The ATS controller features the following adjustable protections:
-OVER and UNDER voltage protection for the MAINS
-OVER and UNDER voltage protection for the GENERATOR
-OVER and UNDER frequency protection for the MAINS
-OVER and UNDER frequency protection for the GENERATOR
-OVERLOAD protection for the LOAD
You can adjust or disable each protection. Each protection features an adjustable bypass timing. In case of a direct short circuit, you must limit the flow of the power from the MAINS and from the GENERATOR. This could be done by inserting circuit breakers of suitable size on the MAINS circuit and on the GENERATOR itself. Assuming you will make a 60KVA ATS panel, the nominal current is 100A. In this case, you must limit the maximum current to 120A. A contactor with a 100A rating may sustain an instant short circuit current up to 5000A.
ATS PANEL PROTECTION
- Always consult the international standard IEC 61439-1-2-34-5-6-7 IEC 60529
- Keep a reasonable distance between cables that carry 400V utility power and low-voltage cables committed to controlling the engine. This will avoid problems in case of severe lightning.
Do not underestimate the panel's maximum operating temperature. Consider proper de-rating of the electrical parameters. A wrong calculation of the size of the cables, terminal blocks, or contactors' nominal current can produce a dangerous overheat.
- Always limit the current into the panel, from utility power and generator, according to the AC1 rating of the contactors and according to the size of cables and terminal blocks. In case of a short circuit, when the automatic protections fail, you can trust an additional external overcurrent protection (e.g. circuit breaker). Doing so will preserve the panel's integrity even in a direct short circuit.
- Always protect the cables connected to the battery plus with the appropriate fuse. A short circuit on the battery cable can reach several hundred amps.
- Always use pilot relays connected as close as possible to the engine.
- We recommend using a mechanical interlock and auxiliary electrical interlock on the contactors.
- Test the automation of the engine and generator before commencing the connection of utility power and generator.
- Before connecting the final LOAD (e.g. the building) always make a test using some lamps. In this way, you are sure that all connections are very well done.
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