Contactor Application for Interrupting a Fault

[majesus]

For a project, we have a 2MVA XFMR (4kV/600V) that has a primary feeder protection that consists of a contactor with a 735 Relay and a 300E fuse.

The short circuit rating on the primary side is no more than 4kA. (The application is a waterpump house 2km away fed by a 2MVA XFMR powering some large pumps.)

Looking at a GE 400A 4.16kV Vaccum contactor (Contactor CR193D, I shall paste the ratings at the end of my post.) It says that it is able to withstand 1 second @ 6000A and has a max opening time (max mS) of 50mS

Question: In this schenario (given the 4kA Short Circit) is it possible to use the contactor to open the fault. And can it break the fault in 50mS? (THAT IS FAST.)

Can this be done? I suspicion and I can't find information on contactors being used to open fault conditions and GE's datasheet for the contactor is vague on this regard.




Contactor Ratings:
Source (pg 15-4)

http://www.geindustrial.com/catalog/buylog/14_BL.pdf

Contactor Ratings—CR193B and CR193D (400A)
Short-time current (amps)
30 seconds 2400
1 second 6000
Impulse withstand (kV) 60
Dielectric strength (kV) 1 minute 18.2
Switching frequency (ops/hour) 360
Mechanical life (ops) 2,000,000
Electrical life (ops) 1,000,000
Closing time (max. ms) 350
Opening time (max. ms)
switched at coil 50
Pick-up voltage (% of rated) 85% max.
Drop out voltage (% of rated) 10%-65%
Control voltage (volts) requires
rectification 110/115 AC
Control circuit burden (VA)
Closing 175
Hold-in 30
Contactor weight 75 lbs. (35 kg)
Standards applicable UL 347
NEMA ICS 3, Part 2

 

[jghrist]

This contactor is for controlling the motor, not for fault interruption. Fault protection is provided by the fuse. The 6000A withstand means that the closed contactor can withstand 6 kA for one second, not that it can interrupt 6 kA.

 

[majesus]

Fair enough... How about then a different contactor: The HCV-5HA 7.2kV made by Toshiba

Table 2
General Application and Load Data
3Ph XFMR: 3MVA @ 4.0-5.0kV

On page 9,
Interrupting Capacity
7000A RMS Symmetrical @5000V Max.
Opening Time 20-30 ms

http://www.toshiba.com/ind/data/tag_files/HCV-5HA Instruction Manual_596.pdf

 

[majesus]

This brochure tabularized the specs nicely

http://www.toshiba.com/ind/data/tag_files/Low & Medium Voltage Vacuum Contactors Brochure_2602.pdf

 

[DrDrreeeaaa]

hhmm. Contactors are control gear, not switchgear.

From 'Practical Power Distribution for Industry' by Jan de Kock, Cobus Strauss:

'It is important to remember that contactors are designed fur frequent load control operations and NOT to interrupt fault currents. Moderate overload currents(up to approx 120 140%) may be interrupted by a contactor, but certainly not short-circuit currents. Therefore, contactors should not be used for protection purposes, and the contactor itselfshould be protected against fault currents'

 

[DrDrreeeaaa]

majesus, that reference was part of a google books preview.

http://books.google.com.au/books?id...&hl=en&sa=X&oi=book_result&resnum=4&ct=result

 

[majesus]

Thanks 123MB... yeah I googled it and found very similar explainations before I posted this question.

But now I got curious about this idea... Following Toshiba's datasheet, I don't see why this wouldn't work for this situtation? The datasheet specifically says it can interrupt a fault current of 7000A RMS Symmetrical. If your fault current is less and the contactor has an opening Time of 20-30 mS... (say 65mS if you include fault sensing, reaction time fo the relay, etc...) it seems the contactor has all the advantage of a circuit breaker... without the CB's cost. Not to mention you can coordinate it with the downstream using the 735 Relay.

I'm just interested in these kind of things... Please if anyone can shed some light, I would like to know.