Promoda Switchgears Pvt. Ltd

An ISO 9001 : 2008 Organisation

Manufacturer of Electrical Control Panels, Instrument Panel, PLC Panel, AC/DC DRIVE Panel.

Frequently Asked Questions

1) Can my VRN2a/6a unit be close coupled onto an Oil filled transformer ?

Yes, our units are supplied with a flange for direct connection onto an ESI transformer.



2) What is the height of the transformer mounting flange on a VRN2 / 6a ring main unit ?

The height from the floor to the centre line of the T-off bushings can be set at 1100 mm, 1320 mm or 1402 mm. Other heights are available on request.



3) My ring switch is in the earth position but I cannot release the star bar to carry out a cable test.

Ensure that the selector is in the centre position with the access shutter closed. If the problem persists contact our After Sales and Service Department for advice.



4) I have completed a cable test on my unit but am unable to move the selector to switch out of earth.

Check that the star bar is fully closed; if not the interlock will prevent the shutter from opening. If the problem persists contact our After Sales and Service Department for advice.



5) Can I have Earth and Test on the circuit breaker of my unit?

This feature is available on our VRN6a, VRE6a and VCE6a units.



6) The pressure gauge on my equipment is in the red area. Is it still safe to operate ?

We do not recommend our units are operated with the gauge in the red area as the SF6 may have become contaminated. However, our units contain a vacuum circuit breaker and will therefore operate safely under fault conditions. If the pressure gauge on you unit is in the red area please contact our After Sales and Service Department to arrange a site visit.



7) The pressure gauge on my unit appears to have a liquid inside but is not to the top of the gauge. Is this leaking ?

This is a viscous damping fluid and is normal. The air gap is to allow the liquid to expand at high temperatures.



8) The gas level in my unit appears to be fluctuating over time. Is this a problem ?

The gauge on our unit measures gas pressure. This will naturally fluctuate as the ambient temperature changes. As long as the needle is not in the red area this is perfectly normal.



9) Can I have top entry cable boxes on my unit ?

Our cable boxes are designed so that they can be inverted for top entry.



10) What cable gland plates are fitted to the ring main units ?

We have a variety of gland plates which can be fitted to our units; single hole, 3 hole or blank. They are manufactured from either steel, brass or aluminium depending on the site requirements.



11) Where are the cable connection points on the ring main unit and what type of connections are available ?

The bushings for each ring switch are located either side of the unit. Both sets of bushings are type C with in-line bolted connections M16 threaded in accordance with EN50181. The T-off bushings are located at the rear of the unit and are in-line bolted connections M12 threaded. All tee-off bushings are fitted with white stress relief collars which must not be removed.



12) What torque setting should I use for the bolts connecting the cables to the bushings ?

The torque settings are 75 Nm for the ring switches (M16 bolt) and 35 Nm on the T-Off (M12). We also recommend that a minimum of 1.5 x thread is screwed into the bushing (eg screw 18mm into a M12 hole).



13) What is the maximum cable size I can fit to the ring main unit ?

Our units can accept a 300 mm2 three core cable or 3 x 500 mm2 single core cables in each cable box.



14) What cable glands are supplied with the ring main unit ?

We can supply a variety of glands with our equipment. These include plain tube, brass wiping, heat shrink and compression glands. Please contact us to discuss your requirements.



15) What cable glands are supplied with the ring main unit ?

We can supply a variety of glands with our equipment. These include plain tube, brass wiping, heat shrink and compression glands. Please contact us to discuss your requirements.



16) What type of ring main units and protection do I need to protect my transformer?

For 11 kV applications we would generally recommend the following:
< 200 kVA: SFRMU with HV fuses
200 kVA 1600 kVA: VRN2a with TLF
>1600 kVA: VRN6a with relay

For specific advice please contact our Technical Department to discuss your requirements.



17) My relay protected ring main unit wont trip when I secondary inject it. I suspect its the relay ?

Check that the settings are enabled correctly in the relay. Make sure the injected current is correct according to the IEC curves. If necessary isolate the phase sensing element under test in the relay. For advice on setting the relay please contact our applications department.



18) I have a unit using TLF protection. What rating of fuse should I fit to protect my transformer ?

The following table gives fuse ratings for most common transformers. For other ratings please contact our technical department for advice.



19) What voltage is needed to operate the remote trip coil on my unit ?

We can supply trip coils to operate between 24 v 110 v DC and 110 v 240 v AC. If you are unsure which of these options you have fitted, please contact our After Sales and Service department with the serial number of your unit and they will be able to confirm the specification.



20) What is the maximum cable size I can fit to the ring main unit ?

Our units can accept a 300 mm2 three core cable or 3 x 500 mm2 single core cables in each cable box.



21) What cable gland plates are fitted to the ring main units ?

We have a variety of gland plates which can be fitted to our units; single hole, 3 hole or blank. They are manufactured from either steel, brass or aluminium depending on the site requirements.



22) Do I need a battery charger in a substation to operate the relay protection/tripping device on my ring main unit ?

Most units supplied by Lucy Switchgear are fitted with TLF or self-powered relay protection; in these cases no auxiliary supply is required. If you are unsure which of these options you have fitted, please contact our After Sales and Service department with the serial number of your unit and they will be able to confirm the specification.



23) What voltage is needed to operate the remote trip coil on my unit ?

We can supply trip coils to operate between 24 v 110 v DC and 110 v 240 v AC. If you are unsure which of these options you have fitted, please contact our After Sales and Service department with the serial number of your unit and they will be able to confirm the specification.



24) What torque setting should I use for the bolts connecting the cables to the bushings ?

The torque settings are 75 Nm for the ring switches (M16 bolt) and 35 Nm on the T-Off (M12). We also recommend that a minimum of 1.5 x thread is screwed into the bushing (eg screw 18mm into a M12 hole).