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Topic Title: Electrical switchgear intrusive physical inspection schedule
Topic Summary: Feedback request
Created On: 23 January 2013 07:23 PM
Status: Read Only
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 23 January 2013 07:23 PM
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tony1234

Posts: 8
Joined: 31 October 2003



Hi there

I would like to engage with people on what they are doing and frequency of physical inspections on low voltage power distribution boards. The trend is to move to non-intrusive such as thermal imaging etc. However, these are deemed more secondary inspections and supplementary in nature. HSG 230 and G3 guidance point to intrusive physical inspections still required. So the questions I have and need feedback on are the following please:

1. What level of physical inspections and frequency are workplaces undertaken at present? Or not?

2. Thermal imaging positive and negative outcomes and justification to reduce physical inspections?

Peoples insights would be helpful

Regards
Tony

 30 January 2013 10:40 PM
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MickeyB

Posts: 181
Joined: 18 January 2003

In reply to item 1, for a 'well run' commercial job every 12M or the 'annual shutdown' is typical.

The work for LV typically involves:
a) ACB 'testing' via the manufacturers test point/ equipment..... or on units with seperate relays secondary injection.
b) MCCB operation '3 or 4' times by hand and press the manual trip..... if available.
c) Check mV drop across MCCB terminals with MCCB closed... to check contact/ cable connections.
d) Check mV drop across ACB terminals with ACB closed...to check....
e) Take some covers off and check copper bars and CT's etc... mV drop test across joints.
f) Hoover the TX pen.... check for partial discharge on the HV/MV side cables... visual check LV bars/ mV drop test on joints
g) Check EPO/ change over operation on ACB's etc... generator/ UPS
h) Test REF relay manually 'with pen' if MCAG 14.....

Basically have a good look round and test the protection. Protection doesn't need testing every year, but most people do....

Item 2, ok if you have kit designed for it.......keep good records of results and can pick up on the changes in temperature..... also it needs to be on load or resonable load to show up any problems......

Most switchboards or DB's are not designed for thermal imaging with covers on..... then you have the issue with taking covers off live and operational risk..... if designed for imaging then you will have a secondary perforated screen behind the outer cover.....'cyclops' are anoher method or if you want the 'full service'..... adopt the TEGG testing methodology and include ultrasound testing...... get a Doble test on your TX if you want the works.....
 04 February 2013 08:41 PM
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dlane

Posts: 684
Joined: 28 September 2007

The physical inspections carried out tend to be based around our maintenance history and the criticality of the plant involved.

Our main LV ACB Incomers are exercised yearly and inspected every 2 years based around the manufacturer's inspection recommendations (IR and ductor tests, contact inspection, regrease mechanism, contact gap measurement, charging spring measurement, terminal tightness etc). We also carry out timing on the breaker mechanism.
The protection relays for theses are tested every 2 years based around the amount of failures we have had. We have upgraded to some digital relays which seem to be more reliable. The arc protection systems are tested every 4 years due to accessibility.

Switch fuse incomers are exercised yearly and usually inspected every 4 years. Just basic cleaning of contacts, regrease mechanism, terminal tightness etc.

The smaller motor control centres are inspected anywhere between annually to every 4 years depending upon our maintenance records and their useage. Includes IR test of motor, terminal tightness, contact inspection if applicable, calibration of transducer etc.

LV busbars are inspected every 4 years. This is mostly a visual inspection and clean, joint inspections where they are accessible.

We have used thermal imaging on the ACBs but don't really gain much information from the images. All the panels are solid steel enclosures, so thermal imaging isn't effective.

We have used thermal imaging on transformers as routine maintenance but for us it hasn't added much value. It certainly hasn't made us postpone any physical inspections due to the results we have seen as it doesn't tell you if arcing contacts are worn or grease is hardening in the mechanisms.

Kind regards

Donald Lane
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