Surge arrester location for Motor and Transformers 1

[NickParker]

Surges arrester for Motors/Transformers:

To be installed in the motor feeder (at the switchgear location) or at the Motor terminal box?
To be installed in the transformer feeder (at the switchgear location) or near the transformer?

 

[Gr8blu]

For the motor manufacturer. the answer is ALWAYS "in the motor terminal box". This is because they aren't interested in protecting the system, just their own equipment.

Most North American large industrial facilities have the protection installed at the motor terminal boxes - especially for larger power critical machines that would take a long time to repair or replace. You might see a gear-mounted arrestor-cap combination if the gear was feeding an easily-replaceable or less-critical machine, or if the gear was in very close (< 10 m) proximity to the machine.

Converting energy to motion for more than half a century

 

[waross]

The impedance of the motor feeders helps absorb and attenuate surges.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[dpc]

Preferred location (by far) is at the equipment. This provides the best equipment protection.

 

[jraef]

Lust be careful with surge cap locations if the motor will be used with a soft start or VFD…


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

 

[wcaseyharman]

What drives the need for surge arrestors and capacitors on motors? Voltage class? Length of cable? Winding type? (Bar versus coil winding)
In our generating plants the generators and main transformers all have surge protection, but I haven’t seen it for our motors, and only at the main switchgear, so I am curious when it would be applied.

 

[Gr8blu]

@wcaseyharman
Let's look at the OP's original posted image. Neither the gear nor the load (motor) is shown, so let's assume the breaker/gear connection is just off-image to the left and the motor is off-image to the right. If the distance "across the image" is small, the likelihood of an event occurring between gear and load is pretty small. This would correspond to most generation facility layouts, where the "across image" distance might only be a few 10s of meters. However, for a large industrial facility (think petrochemical, pulp and paper, mining, or metal rolling) or a dispersed generating facility (onshore or offshore wind farm, tidal power, solar plant), the distance between the gear and the machine may be anywhere from 500-2500 m - or even more. How often do you think an event might happen in that kind of distance? Particularly with all the other associated equipment (overhead cable runs/trays, light poles, process flow routing, cooling towers, cranes, etc.) located in between?

The major reason for surge caps and/or arrestors is the ability to protect critical equipment from the likelihood of a (substantial) transient event, such as a lightning strike or - in some cases - a switching transient (like an auto-transfer between multiple feeder busses).

Converting energy to motion for more than half a century

 

[waross]

When a transient event is suppressed, only a part of the associated energy is dissipated in the arresting device.
Much of the energy is mitigated and dissipated in the impedance of the conductors between the source of the transient and the surge suppressor.
In almost all installations, the greatest percent of impedance is the local conductors to the motors.
So, the closer to the motor, the more impedance in the circuit and the less energy the arresting device must dissipate.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[dpc]

We routinely specified surge arresters and caps for all medium-voltage motors. Expensive and long-lead time equipment. And more surge issues at higher voltages.

 

[wcaseyharman]

Is there a distance or exposure rule of thumb that’s common in the industry, or is left up to the engineer’s preference?