3 Phase motors w/capaitor?

[mcs666]

I am involved with rebuilding an older European machine and have found what looks to be capacitors across the 3 phase motor legs. I have never seen this before and was wondering if anyone can give me some insight. The motors have a device, Lutze #LRC-M1 across the motor legs, which I think is a capacitor bank. Any input would be greatly appreciated.

 

[DRWeig]

Built-in power factor correction?

Best to you,

Goober Dave

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[mcs666]

Found that the devices I originally stated are actually motor suppressors.
I have never used them and was wondering what their purpose is and if really beneficial.

 

[magoo2]

Sounds like they are being used as surge capacitors. Capacitors will slow down the rate of rise for incoming surges and the result is less harmful to the motor insulation. They are typically used in combination with surge arresters.

What is the rated motor voltage?

 

[electricpete]

US standards (IEEE Std C62.21™-2003) allow for connecting surge protective devices (surge capacitors for sloping and possible surge supressors for clamping). They are connected phase to ground at the motor terminals, presumably to protect against phase to ground and common mode transients.

Protection connected between phases would seem to be intended to protect against differential mode transients. I tend to think if the motor is supplied by shielded cables (as common for medium voltage motors), then there is no differential mode path to the motor.

Just curious now (since I've never heard of this). What is the motor hp and supply voltage? Are you supply cables shielded?


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(2B)+(2B)' ?

 

[mcs666]

The suppressors (RC Modules) are connect phase to phase.
Supply voltage is 480VAC.
Motor KW are as follows:
2.3/3.1 KW
0.12 KW
0.75 KW
0.12 KW

 

[jraef]

From my experience it's an old practice intended to help protect motors from grid transients but has been abandoned for the most part now. The only time I have seen it done on small motors like this is when they are on machines going to parts of the world with unstable / unreliable power. They can however cause serious problems if left in place when VFDs and Soft Starters are connected to the motors, which is much much more common now than it was 20 years ago. But because most people don't know what they are, they tend to leave them in and discover the pitfalls when the power devices in the solid state controllers fail on short order.

I still see a lot of older specs for large MV machines that call for them, even when being controlled by SS controllers, because a lot of the specs are older and nobody has bothered to update them. GE used to include them if you asked for them or not on their MV motors and sometimes still do, which causes extra work in the field to remove them.

"Will work for (the memory of) salami"

 

[mcs666]

Thanks to all for the input.
Your comments have verified my decision to remove them.
Wish cleaning up the wiring numbering was as easy!