Retrofit T300 Underground FCI in Padmount Switchgear (US)

[Chris_Kerr]

First time enlisting help from Exchange. 

We have a customer we are working with to try to develop a solution to use the T300 as an advanced underground FCI. 

Is it even feasible to use the T300 in a retrofit application where no sensors (CT's, PT's, or power to power a PS50 or DC power) is available? 

I'm curious what people's thoughts on the best way to integrate with for example S&C PME / PMH switchgear or some other manually operated gear if we want to get fault detection and communicate in real time (and the other benefits of the T300)?

[JYPOC · Accepted solution]

Hi Chris,

First, it is important to remember that the SC150 module performs a 3-phase MV fault detection (ANSI 50/51/67 and 50N/51N/ 67N) and not a single-phase one.

Then to answer your questions:

1. To detect MV fault currents on solidly grounded MV network (typical US case) or resistor-earthed, you only need to add 3 phase measurement CTs (ranging from 50 to 1250 A on the primary side, and 1 or 5A on the secondary side). In addition, if you want to detect SEF down to 0.5 A, you will also need a 4th CT (core balanced CT, preferably 50/1 or so). Outside NA, we can offer 500/1 Class 1 or 3 CTs as they are fitted for the MV switchgear used: they have never been tested in the US (tbc) so I don't believe we can propose them. So you'll have to purchase these CTs from local US suppliers.

2. To detect directional earth faults and/or perform PM/PQ measurement, it is required to have 3 single-phase voltage measurements.

Outside North America, the MV switchgear is always fitted with a capacitive divider connected to the 3 MV capacitors of the MV switchgear. SE provides something called VPIS-VO V3 (voltage presence indicator system with voltage output) while German-influenced competitors utilize VDS (voltage detection system) but they can both be connected to the SC150-LPVT to perform directional fault detection, PM/PQ measurements, ANSI 29/59, ANSI 47BC and ANSI 32P (active overpower direction detection, very useful when many DER are deployed).

For retrofit in the US, I see two options: install either 3 LPVTs (1 per phase) or one 3-phase VT to the MV functions on which it is required to perform the above-mentionned features.

Regards,