HV Neutral Conductor 1

[timm33333]

I have a question about the voltage rating of neutral conductor for solidly grounded 230kV shunt reactor. NEC 250.184(A)(1) states that for solidly grounded systems greater than 1kV, the insulation of neutral conductor has to be minimum 600V.

So for 230kV solidly grounded shunt reactor, the insulation of the neutral conductor (from star point to ground) has to be only 600V. Is it correct? Thanks.

 

[cranky108]

If you are working with 230kV, and using NEC, and not NESC, I'm not sure where you are.

Most reactors that maybe air core, would have a fence around them for safety.
Reactors that are under oil, would be treated like a transformer.
Hope that helps.

 

[timm33333]

NESC does not give information about neutral conductor. Which standard (IEEE or IEC) provides information about insulation level of neutral conductor for solidly grounded 230kV oil filled shunt reactor (or transformer)?

 

[davidbeach]

In a utility substation I wouldn't expect it to be insulated.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[timm33333]

There is also IEC 60076-3 section 7.4 which says that for solidly grounded system, when transformer voltage is more than 72.5 kV then the test voltage for neutral terminal has to be minimum 38 kV (Um ≥ 17.5 kV). Um is maximum system voltage for which equipment maybe used.

It is not clear but it looks that in IEC world: for solidly grounded systems greater than 72.5kV, the insulation level (Um) of neutral cable has to be minimum 17.5kV. What do you guys think about it?

 

[timm33333]

IEC 60076-3, 7.4.2.1

 

[jghrist]

The requirement is for the transformer terminal, not for the neutral conductor. The terminal is insulated so that the neutral can be disconnected from ground for testing.

 

[che12345]

Dear Mr. timm33333 (Electrical)(OP)11 Jan 23 16:37
"....I have a question about the voltage rating of neutral conductor for solidly grounded 230kV shunt reactor. ..... So for 230kV solidly grounded shunt reactor, the insulation of the neutral conductor (from star point to ground) has to be only 600V. Is it correct? "
1. I take it that the length of the conductor in question is :
(a) from the shunt reactor to the ground. This conductor is NOT Neutral conductor. It is a grounding conductor; maintained at ground potential.
(b) from the transformer start-point (Neutral) to the shunt reactor. which is NOT maintained at ground potential.
2. For above 1 (a), the grounding conductor can be bare. It is intended to be connected to the grounding electrode, which is always bare. If insulation is applied for other than electrical safety reasons, 600V would be acceptable.
Che Kuan Yau (Singapore)

 

[Amit Bajpayee]

The HV (high voltage) neutral conductor is an electrical wire conductor that carries current in a three-phase electrical system where the neutral point is grounded. It is a component of the electrical system that is used to provide a return path for current flowing in the system. The neutral conductor is typically connected to the neutral point at the transformer and is typically connected to the earth at the substation. In some systems, the neutral conductor is also used to provide a reference point for measuring voltage and current.

https://agnisolar.com/

 

[timm33333]

"""If insulation is applied for other than electrical safety reasons, 600V would be acceptable."""

I think electrical safety would not be an issue here because it is a grounding conductor which connects the star point of shunt reactor to the ground. However insulation might still be required to avoid corrosion and to insulate this grounding conductor from other metal parts like cable trays; and for that 600V insulation should be sufficient.

 

[che12345]

@ Mr. Amit Bajpayee (Electrical)
Mr. timm33333 : "....So for 230kV solidly grounded shunt reactor, the insulation of the neutral conductor (from star point to ground) has to be only 600V. Is it correct? "
I take it that it is NOT a Neutral conductor. It is a Grounding conductor, connecting to the ground electrode. NOT distributed as Neutral.
With this clarified., pleased advise your learned opinion.
Che Kuan Yau (Singapore)

 

[prc]

In the case of solidly grounded Shunt Reactors, the minimum insulation level of the neutral terminal shall be > 17.5 kV Class ( 38 kV AC test voltage) as per IEC.

EHV shunt reactors are used in two modes- bus reactors in substations and line reactors for compensating the capacitive MVAR of transmission lines. In the former case neutral is solidly grounded and a 38 kV insulation level is sufficient. But the neutral of the line reactors is usually grounded through a small inductor(neutral grounding reactors) for single pole reclosing. The Neutral reactor will compensate for the capacitive current during LG faults. ( to reduce arcing)

In the case of EHV line reactors (400-800kV), the neutral insulation level is 145 kV class (550 kV BIL) to take care of the neutral over-voltages during LG faults. In India, for interchangeability, we provide 550 BIL for the neutral of all EHV shunt reactors.

 

[timm33333]

As mentioned above, we are talking about the insulation of grounding electrode conductor which connects the star point of shunt reactor to ground. We are not talking about the insulation of neutral terminal of shunt reactor.

 

[prc]

Normally this grounding bus from neutral bushing of reactor to ground electrode is taken over 17.5 kV pin insulators to avoid flashing over to the tank or earth.

 

[che12345]

Dear Mr. timm33333 (Electrical)(OP)16 Jan 23 19:50
@ prc (Electrical)16 Jan 23 16:25
Thank you for your learned advice. Please take note that Mr. timm33333 stresses:
"...As mentioned above, we are talking about the insulation of grounding electrode conductor which connects the star point of shunt reactor to ground. We are not talking about the insulation of neutral terminal of shunt reactor."
[/highlight]
Che Kuan Yau (Singapore)

 

[cranky108]

The neutral is not always grounded. In these cases, the neutral should be insulated the same as the phases.
For cases where the neutral is intended to be grounded, it is our custom to use a 15kV bushing, that is common with what we stock for spares.
I say 15kV because most of what I do is in substations. Distribution transformers are so common that if we stock spares (I don't know, but I expect so), there are likely several types.
Also transformer core grounds are also on 15kV bushings.

 

[timm33333]

What kind of connector can be used to connect the 600V (or bare) grounding cable to 15kV neutral bushing?

 

[prc]

In the case of single-phase transformers, flexible connectors. In other cases flexible copper or steel strips are used without extra connectors.