Trip circuit supervision relay for 5MW motor breaker
Trip circuit supervision relay for 5MW motor breaker
(OP)
In our plant has been decided (because of bad design) to replace fuse-vacuum contactor protection scheme for a motor with breaker protection. The motor is 5MW, 11kV. For this purpose an entire switchboard will be changed.
The existing motor protection relays will be re-used. One of the relays is a multifunction protection relay (protecting the motor for: locked rotor, motor overload, too long start, etc.) and the other relay is a trip-lockout relay.
My question is: do we need as well with the new breaker protection sheme of the motor, to have a trip circuit supervision relay ?
The existing motor protection relays will be re-used. One of the relays is a multifunction protection relay (protecting the motor for: locked rotor, motor overload, too long start, etc.) and the other relay is a trip-lockout relay.
My question is: do we need as well with the new breaker protection sheme of the motor, to have a trip circuit supervision relay ?





RE: Trip circuit supervision relay for 5MW motor breaker
A little clarification please. By "trip circuit supervision relay", do you mean a relay that tells you whether or not you have power to your trip circuit?
Mike
RE: Trip circuit supervision relay for 5MW motor breaker
RE: Trip circuit supervision relay for 5MW motor breaker
In UK parlance, a TCS relay allows a low current to bleed through the tripping coil, thus proving that the tripping coil and any contacts or connectors other than the actual trip relay contact itself are intact and that the tripping battery source is available. The current is far below the actual operating current of the coil, and has no practical effect on breaker operation.
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I don't suffer from insanity. I enjoy it...
RE: Trip circuit supervision relay for 5MW motor breaker
Ah...gotcha.
hottip:
In that case...what stevenal said.
Mike
RE: Trip circuit supervision relay for 5MW motor breaker
RE: Trip circuit supervision relay for 5MW motor breaker
Generally a solenoid is used. The basic idea is that the coil for the undervoltage device is connected in parallel with the entire trip circuit, thus sealing it in when potential is present. If potential is lost, the coil deenergizes. A spring then causes the solenoid plunger to extend and operate a cam or plate connected to the circuit breaker's tripping mechanism.
This prevents a situation in which your protective device attempts to clear a fault in the motor circuit, but cannot because of loss of power to the trip circuit. The downside is that disruption of power to the trip circuit for any reason (including accidental loss due to maintenance of nearby systems, etc.) WILL cause your motor breaker to trip open.
Generally speaking, anytime that I've seen a circuit breaker directly controlling a motor (rather than a starter), there has been some form of failsafe tripping protection installed (in your case a TCS relay).
Hope this helps,
Mike
RE: Trip circuit supervision relay for 5MW motor breaker
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I don't suffer from insanity. I enjoy it...
RE: Trip circuit supervision relay for 5MW motor breaker
Thank you very much for your answers.
@applekor: the undervoltage contact was in the old scheme (fuse-contactor) and will be present as well in the breaker new design.
I found this with google:
'A TCS relay is used to monitor the integrity of a circuit breaker's trip coil and associated wiring. Such a relay may be connected to monitor the trip circuit with the breaker in both the open and closed positions, or just for the closed position.
A TCS relay issues an alarm if it detects trip circuit supply failure or circuit breaker tripping mechanism failure.'
My question is: is it normal for a TCS relay to TRIP the breaker if the TCS trips? I mean in case of TCS detecting 'no supply voltage present' (for example) and will give an alarm, in the same time will trip the motor breaker?
RE: Trip circuit supervision relay for 5MW motor breaker
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I don't suffer from insanity. I enjoy it...
RE: Trip circuit supervision relay for 5MW motor breaker
If the breaker has a true undervoltage release, it can trip without external control power - in fact you can't stop it from tripping - that's the downside of the UV release. It's always there when you need it, but it's also always there when you don't need it.
RE: Trip circuit supervision relay for 5MW motor breaker
RE: Trip circuit supervision relay for 5MW motor breaker
There is a small possibility that the breaker of one of the motors not to open when is required if undervoltage shall occur. In this case I believe that the very expensive 5MV motor can be damaged (I mean the bars from the rotor can be affected by the powerful momentul generated by the voltage drop and by the re-apparition of a normal voltage)
RE: Trip circuit supervision relay for 5MW motor breaker
RE: Trip circuit supervision relay for 5MW motor breaker
I would like to add a note to your comments. Depending on the manufacturer and model of the circuit breaker there is still likely a manual, mechanical trip on the circuit breaker frame. Obviously this doesn't help you much in a fault situation on the motor leads or windings, but you WOULD still (technically) have motor control.
As for the undervoltage trip, most modern multifunction relays (should) allow you to specify an undervoltage function disable that you can logically implement into a startup scheme.
stevenal:
I agree. DC is the best to use in these situations. If this is not an option, hottip, then you might consider adding an auxilliary (gasoline/diesel) generator or battery + inverter setup into your trip circuit supply for use during black starts or outages.
Regards,
Mike
RE: Trip circuit supervision relay for 5MW motor breaker
On the other hand, it was pointed out to me in a previous thread that on a large breaker the trip solenoinds may be so large that power consumption becomes an issue if the solenoids are continously energised. Hence battery banks and shunt trips on large installations.
respectfully
RE: Trip circuit supervision relay for 5MW motor breaker
RE: Trip circuit supervision relay for 5MW motor breaker
My question is related with the faults that can happen inside the motor and the breaker will not be tripped because of the fault with the tripping circuit itself.
There is nobody in HV room, so such an alarm from a TCS relay can go unnoticed.
The other scenario can be like this:
Breaker on, motor working => suddenly the tripping circuit is faulty, TCS alarm which can go unnoticed => suddenly under voltage situation in the plant power system => the undervoltage relay gives command to the breaker to open => breaker cannot open (trip circuit fault) => the undervoltage condition of the plant finished (so again will be normal voltage of the power system) => normal voltage re-applied for an electrical motor which was not working at the nominal rpm (because of undervoltage) => high torque applied for the rotor shaft => motor damaged ????
Sorry for this long story but I'm really interested of your experience wich such a system. I do not have an experience with motor breakers.
RE: Trip circuit supervision relay for 5MW motor breaker
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I don't suffer from insanity. I enjoy it...
RE: Trip circuit supervision relay for 5MW motor breaker
If the motor is a very vital process equipment, you may want to consider also providing circuit breakers with dual trip coils with a breaker failure relay.