Re-commissioning after the system is kept off for a prologed duration

[krisys]

We have five (5) nos. of 11 kV Ring Main Unit (RMU) Loops supplied from a 11 kV container substation. Each loop (distribution Ring) has two feeders from the same substation. Even if one feeder or one RMU is one outage, the other RMU loads can be supplied. Needless to say without a redundancy of source!

The RMU is feeds one transformer rated 11kV/433V, 150 kVA. The downstream has one main Distribution Board. The main Distribution Board feeds the loads such as UPS, 5.5kW motor driven pumps, Motor operated valves etc.

We have situations where we may sometimes need to keep the RMU and the Loads connected to the RMU off for a prolonged period of time, say one (1) to eight (8) months. In this case, while resuming the power supply to the RMU, do we need to re-commission the system or we can just energize the system and take it into service?

Is there any regulatory requirements or industry practice governing this aspect.

In my opinion, it makes sense to perform some basic tests/inspection before energizing the system after a prolonged duration n outage. But up to what level is what is intriguing me.

 

[crshears]

We have situations where we may sometimes need to keep the RMU and the Loads connected to the RMU off for a prolonged period of time, say one (1) to eight (8) months. In this case, while resuming the power supply to the RMU, do we need to re-commission the system or we can just energize the system and take it into service?

You don't say why this is necessary...

Within the utility that employs me, whenever it is possible to do so, idle but not de-commissioned equipment is kept on potential from one end to continually prove serviceability and, in the event of fault, promptly notify the controlling authority of said condition.

Since there will typically be zero customer impact if the equipment under consideration sustains a fault, any auto-reclosing features for it are usually blocked and caution tagged for the duration of such status.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[davidbeach]

Our practice is that underground cable idle for more than 30 days since last test or last time energized must be tested again prior to being energized. As crshears says you can know how it’s doing if it’s energized but you know nothing about it if it’s dead.

 

[krisys]

crshears, David,

My domain is an offshore oil field. In the middle of the sea, there is a large platform (called central platform) where the main power is being generated for the oil processing facilities within the central platform. The power generation capacity here is about 70MW capacity.

There are small platform structures to support the oil well heads with some instrumentations, Motorized valves, drains, chemical injection pumps etc. Let us call it as Well Head Towers (WHT). Such WHTs are spread across the oil filed of 40 km x 40 km field about 4 km apart from each other, numbering about 120. The power required is only a small amount say 40kW for each WHT. So the Ring Main Units (RMUs) are used to feed these WHTs each loop is covering about 10 WHTs.

During the operation of the oil wells, they need to do some maintenance, re-drilling the wells etc. Once the drilling rig enters comes to the WHT, it may remain for few months like 4 to 9 months. So when the rig enters, they need the complete power isolation.

Now once the rig guys hand over the WHT back to the operations (production department) say after 9 months, we need to energize the power to that particular WHT. This will be happening for one or the other towers on a regular basis.

Hope this would give some perspective and understand the background of my query. Now I would appreciate your experience and feedback on the power re-energisation.

 

[davidbeach]

I would say re-test the cable prior to reenergization.

 

[krisys]

But what about the other downstream system, like 11kV/433V transformer, 415V main panel, UPS etc.?

[ul]
[li]Up to what level the testing should be carried out?[/li]
[li]Whether to repeat all the commissioning tests[/li]
[li]or some selective tests[/li]
[li]or only the basic test i.e. insulation resistance measurement?[/li]
[/ul]

 

[prc]

For Transformers, I would suggest IR test and oil BDV if the shut down is more than 30 days.