avoiding power contactor drop off during voltage dip 1

[vijaypandiyan]

Hello all,

During voltage dip in main incomer, power contactors in motor feeders get dropped as its coil supply voltage is taken from incoming supply via control transformer. I have an idea to use ABB YU time delay release which is used to delay the drop off of UV coil in ABB Emax ACBs.

Kindly let me know your comments.

Thanks,
Vijay

Thanks,
Vijay

 

[waross]

There is a point where you may want to drop the contactor out for low voltage.
One instance would be a complete power failure, another may be a sustained low voltage condition.
For some types of equipment safety and or electrical codes mandate a drop out on loss of power.
A time delay won't help if there is not enough voltage to hold the coil in.
Try a UPS with a suitable relay to trip the holding coil on either a sustained voltage dip or a complete loss of power.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[vijaypandiyan]

We don't want to trip the contactor for momentary dip in voltage.
I checked about the holding capacity of the time delay and it is OK to use for this contactor holding value.
Installing UPS is also on the table for talk.

I wanted to know if there is any other alternatives for this.

Thanks,
Vijay

 

[LionelHutz]

Constant voltage or ferroresonance control power transformer.

 

[waross]

If the voltage dips below the coil hold in voltage, you won't be able to hold the coil in with a relay. You must use some form of voltage support.
I like Lionel's suggestion. That will still give you a drop out on the complete loss of power.
Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Use DC control power. Big reservoir capacitor for short duration ride-through, back it up from a battery if needed for prolonged dips or outages.

 

[davidbeach]

Scotty is headed in the right direction, but don't forget to add actual undervoltage protection once you no longer have the inherent undervoltage protection of the coil dropping out.

 

[vijaypandiyan]

Hello all,

Thanks for your replies. I will see if we can go for UPS where installing this time delayed release is not possible due to holding value of coil might exceed the value of this device can supply.

One more question. Suppose I install this time delayed device which can supply to coil of the power contactor for 3 secs from its inbuilt stored power capacitor. Let us consider Pickup power is 200W and holding power is 20W.
When the main power supply drops and power is supplied from this device to the coil of the power contactor, the coil will draw supply using which power? pickup power or holding power?

Thanks,
Vijay

 

[waross]

this time delayed device which can supply to coil of the power contactor for 3 secs from its inbuilt stored power capacitor.???

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

That relay might work, but it doesn't appear you will have much accuracy in how long the coil is held in or ability to trip it exactly when you want.

It says 0.5 to 3 seconds and I don' see any time adjustment in the pictures so it seems to just be a dumb capacitor storage device that will manage to hold the coil for some time before it drops out.

 

[jraef]

Devices like this exist, they are referred to as PORT devices (Power Loss Ride Through). Depending on the duration of the power dip, they add capacitors to the coil circuit.

http://pqsi.com/products/

The down side to this concept is that these devices cannot distinguish between a power loss, and an Off command. So in using them to hold up in brief interruptions, they also end up adding a delay in turning the contactor off, which can be dangerous.

A better option is something that holds up the control power in general, such as the ferroresonant power conditioner or something like a DySC (Dynamic Sag Corrector). Those however are mainly for SAGs, not complete outages. In the case of a DySC, it can hold up for about 0.5 seconds in a full outage.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[RRaghunath]

Shell uses Restart units in their power contactor control schemes. There are two models - one (ERM) just to ride through transient voltage dip/loss not exceeding 200ms duration. The other (TDRM) includes longer duration power loss and includes staggered restart facility with settable time delay.
The ERM maintains contact in power contactor closing circuit for 200ms so that when the power is restored, the contactor can immediately pickup. This can be applied to all the drives without any problem.
Whereas, if the duration is longer, the system requires reacceleration study to be done to decide the groups of motors for staggered restart for applying TDRM.

Rompicherla Raghunath

 

[vijaypandiyan]

@Waross: Yes it is supply power from in built capacitor stored energy.

@jraef: Yes, I thought of that downside you mentioned. That is why in between the coil and this device, we will have start PB contacts in series, so that when you want to stop the motor, this PB will be opened, so that it will immediately cut off the contactor coil from this device to open the main contactor. there will be no time delay in turning contactor off. Do you think this will overcome the downside you mentioned?

@Raghu: Can you send in detail about the TDRM?

Thank you all for wonderful discussions.

Thanks,
Vijay

 

[RRaghunath]

Vijay,
Below is the extract from Shell standard on the subject:
2. The automatic restart facility shall be initiated under the following conditions:
a. Voltage-dip detection level at 65% of Un.
b. Voltage restoration detection level at 90% of Un.
c. Immediate restart after voltage dips  0.2 s.
d. Delayed restart after voltage dips of > 0.2 s with an adjustable maximum of 60 s in steps of 5 s after which the unit shall be not restarted without an external start command.
e. If a second voltage dip, with duration less than 0.2 s, occurs within 1 s after the first voltage dip, a delayed restart command shall be given.
f. The undervoltage memory time buffer shall be at least 4.5 s.
3. The minimum detection time for a voltage dip shall be less than the drop time of the contactor (considered to be 10 ms) therefore ensuring that a voltage dip is detected even after a transient interruption has occurred.
4. It shall be possible to set the maximum dip duration, after which the system will initiate a restart, between 4 s and 30 s.
This longer time may be required if the motor is reconnected to an emergency supply after a power failure in the normal supply.
Many of the modern motor protection relays include this feature, Motor protection relay M102 of ABB for example.
Hope it will help.

Rompicherla Raghunath

 

[Mahmoud-Abdullah]

if you have one incoming for the panel, you can replace the undervoltage coil with a shunt coil and monitor the line voltage by an external relay like 3UG4616-1CR20 Siemens type. the incoming will trip only after the relay picks up and you can delay the pick up by the relay.

Keep Moving Forward

 

[krisys]

Do you want ride through or re-acceleration?

These are two different things used in a process industry. Ride though is for the momentary voltage dips of say 200 mS. The motor shaft doesn't come to stand still. So in the ride through the motor end windings should be capable enough to handle the over voltage due to back emf.

Re-acceleration scheme is one where the normal power fails and the running motors will comes to complete standstill. Now the emergency DG set kicks and brings back the power in say about 10-to 15 seconds. Then the motor should re- start from the zero speed. This is called re-acceleration. If you have multiple motors to re-accelerate, then based on the maximum tolerable inrush on the DG set, the motors will be started/re-accelerated in groups.

Vijay's requirement appears to be for ride-though. It is a commonly asked by many customers. You should get in the market easily.

Hope I made it clear