Motor Protection Standards


Thread Starter


I was studying the relays at our site and noticed the various settings for the protections, such as over current, thermal overload, etc.

Motor ratings: 11KV, 20A, 250kW

I need to verify whether these settings are accurate or not. Where can i find specific ranges/standards for the relay settings for the aforementioned 11KV motor. An example of what I'm looking for is for low stage over current (3I>). I have:

Start current: 1.1 x Nominal Current
Start time: 9 sec
trip pulse: 40 ms

I'm specifically trying to find ranges/standards for the following protections:

- 3 Phase Non directional over current (3I>, 3I>>, 3I>>>)
- 3 Phase Thermal overload (3I thdev)
- Negative phase sequence (I2>)
- Ground fault (Io>)
- Motor start up supervision (Is2t n<)
- 3 Phase Under voltage (3U<)
Get yourself a copy of the NEC (National electrical code manual), or you can google NEC standards and come up with information there.