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FAQs

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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.

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.

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.

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.

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

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

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.

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. 

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. 

Can I have top entry cable boxes on my unit?

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

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.

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. 

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). 

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.

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.

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 Electric 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.

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.

My relay protected ring main unit won’t trip when I secondary inject it. I suspect it’s 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.

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. 

 

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.

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.

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). 

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.

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.

I have TLF protection on my RMU. Can I swap it for a relay protection device

Yes it is possible; please contact our After Sales and Service department to discuss your specific requirements

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.

My relay protected ring main unit won’t trip when I secondary inject it. I suspect it’s 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.

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. 

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.

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). 

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.

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.

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.

I have TLF protection on my RMU. Can I swap it for a relay protection device

Yes it is possible; please contact our After Sales and Service department to discuss your specific requirements 

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 Electric 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.

My relay protected ring main unit won’t trip when I secondary inject it. I suspect it’s 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.

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.

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. 

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.

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 Departmentto arrange a site visit.

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. 

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. 

Can I remotely operate my ring main unit?

It is possible to fit actuators to both the ring switches and circuit breaker of our ring main unit. We also offer our Gemini RTU which can communicate with SCADA systems using a variety of media and protocols. If you have a large number of units you wish to communicate with we can offer a bespoke SCADA system to control and monitor all units on your site.

What voltage is required to operate the actuators on my Ring Main units?

All our actuators operate at 24 volts DC.

I have an automated ring main unit but the ring switch motors won’t operate when given a command from the RTU?

Check the unit is in the service selected position, the manual operation access shutter on the actuator is fully closed and the actuator is plugged into the front panel of the ring main unit. Check the fuse in the control PCB in the marshalling box is intact. If the fault persists please contact our After Sales and Service department

I want to carry out a manual operation on my ring switch but there is an actuator fitted. I have opened the shutter and tried to operate it but it is too stiff?

The actuator will need disengaging to allow manual operation. A mushroom knob is supplied with the actuator. This should be placed on the operating shaft and firmly pressed in to allow manual operation.

My actuator stopped halfway through an operation and is now stuck on the ring switch. How can I remove it?

The actuator will need disengaging to release it from the operating shaft. A mushroom knob is supplied with the actuator. This should be placed on the operating shaft and firmly pressed in to release the actuator and allow it to be removed or the unit to be manually operated through it.

I have an old ring main unit on site. Can I retrofit an actuator to it?

We have a number of retrofit kits suitable for fitting to both Lucy an third party products. Please contact us to discuss your exact requirements.

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