Portable Earthing Leads – Short Circuiting Kits For HV Substations & Overhead Lines

Published 18 Jan 2018

Portable Earthing Leads

 uploaded by Chris Dodds - reading time 5 minutes 

 

This following procedure from TransGrid supports the Power System Safety Rules and its requirements for Portable Earthing assembled under:

 

  1. Making High Voltage Apparatus Safe for Work – Category 5.5; &
  2. Making Overhead Lines Safe for Work – Categories 6.4, 6.5

The following describes Electrical Safety Equipment manufactured by CATU Electrical which has been approved for portable earthing of high voltage electrical conductors. This procedure also includes methods for checking substation and overhead line earthing equipment along with inspection and maintenance procedures.

Date of Issue: 26 May 2016 

Portable Earthing Leads & Systems

An earthing system is a recognised set of components to perform the function of portable earthing for medium/high voltage cables. The components are assembled into either polyphase earthing systems (usually three phase) or single phase earthing systems.

A portable earthing leads and system comprises of:
1. Line End Clamp or Clamps
2. Portable Earthing Leads
3. Earth End Clamp or Clamps
4. Short Circuiting Point (Trifurcating Plate)
5. Connecting Hardware
6. Insulating Sticks

Portable Earthing

Portable Earthing Leads & Kits manufactured by CATU Electrical are for short-circuiting of medium/high voltage power cables and conductors including 11kV/33kV and 132kV.

Prior to the issue of an Access Authority, appropriate earths must be applied to High Voltage Equipment. These are referred to as Access Authority earths under the Power System Safety Rules. Where fixed earthing switches are either not available or not suitable for the planned work, portable earths may be used. Such portable earths can be applied to:

  • overhead tranmission lines
  • substations
  • switchboards
  • underground cables

The objective of Portable Earthing Equipment is to provide a pathway for unanticipated electrical current to flow safely to earth. The current flowing through the earth causes protection systems to operate, tripping circuit breakers and so removing the source of electrical power supply.

The earthing equipment described in this procedure has been designed and tested for use with standard TransGrid conductors and fittings such as stirrups and stubs.

Electrical Safety

Electrical safety guidance about handling portable earthing equipment in substations or near transmission lines:

1. Always carry earthing equipment below shoulder level
2. Ensure that clamps and leads are kept a safe distance from any high voltage conductor
3. Assemble and inspect earthing equipment on the ground
4. Extend or prepare any earthing equipment such as shot gun sticks on the ground

CATU Electrical

CATU Electrical – Thorne & Derrick are the largest UK stockist and supplier of MV HV Electrical Safety Equipment for Substations & Overhead Lines

Portable Earths

Applying Portable Earths

Do not allow any part of the earthing system to encroach on safe approach distances.

1. Where practicable keep the portable earthing leads away from the body
2. Apply earth clamps to stirrup (if provided) or a horizontal conductor where possible
3. Avoid earth clamp application to bushing caps and to braids and
4. Position earth clamp so that tension on the earth lead is minimised

Removing Portable Earth Leads

Earthing equipment is to be removed carefully from high voltage conductors to prevent the equipment encroaching on or coming into contact with adjacent live high voltage conductors.

Discharging HV High Voltage Equipment

Where an electrical circuit could potentially discharge through the earthing system, sufficient time must be allowed between the de-energising of the high voltage conductors and the application of the portable earthing system to permit residual charge to be dissipated.

Equipment Experiencing A Fault

Any medium voltage or high voltage portable earthing equipment for overhead line or substation applications that experience a fault or over current shall be withdrawn from service immediately.

Rating

Check that the rating of the earthing equipment is appropriate for the fault level at the location at which it is to be applied. The equipment used for earthing shall have a fault withstand rating greater than that of the location in which it is used.

Information about the expected fault currents and back-up protection times at particular locations is available from System Operations staff.

Where the fault rating of the location exceeds that of the equipment, multiple earthing sets may be used to increase the rating of the earthing system:

1. In switchyards this information will be included on the High Voltage Preparation and Restoration Instruction (HVPRI);
2. On transmission lines where the fault rating of the line exceeds the fault rating of the earthing set, multiple sets of CATU MT815S earth clamps and associated earth end clamps may be used.

Equipment & Connections

Check that the earthing system is complete, i.e. that all earthing components are present.

Check that all bolted connections are tight and that any electrical connection is positive and mechanically sound. Ensure that earthing leads are sufficiently long for the proposed task.

Inspect For Damage

Ensure that the MV-HV earthing leads and equipment is in a serviceable condition. Any portable earthing equipment found to be defective shall be removed from service for repair.

Connect Earths To Earthing End Point

Connection at the earth end point shall be performed prior to any connection to a conductor.

Use Of The CATU MT-815S Clamp

The CATU MT 815S earth clamp is applied to and removed from conductors using a ‘shotgun’ application stick of appropriate length. Once the clamp is placed onto the apparatus to be earthed, the shotgun stick is removed.

Use Of The CATU MT-815E Clamp

The CATU MT 815E earth clamp is applied to and removed from conductors using the attached CATU CM4130-E insulating sticks.

Use Of The CATU MT-701 Clamp

The CATU MT-701 clamp is a V-shaped cast aluminium earth clamp that maintains contact with the conductor via a spring loaded jaw that is preset by a latching mechanism. The clamp is ‘snapped’ onto the conductor by a quick pulling action that triggers the jaw mechanism. The clamp is designed to be applied to and removed from medium/high voltage conductors using haulage and release cords.

Arming The CATU MT-701 Clamp

Lay the clamp on the ground so that the tail of the tongue points vertically upwards.

Holding the earth lead in one hand to stabilise the clamp, use the heel of your shoe to compress the tongue down against the body of the clamp until it latches. Ensure that the clamp is securely latched before handling.

Applying The CATU MT-701 Clamp

1. Pass the haulage cord over the conductor or through the stirrup by the using a sandbag
2. Arm the earth clamp
3. Hoist the clamp to the conductor using the haulage cord; then
4. Latch the clamp to the conductor with a quick pull on the cord

Removing The CATU MT-701 Clamp

1. Take the weight of the CATU clamp and lead on the haulage cord
2. Pull the release cord until the clamp releases from the conductor
3. Lower the earth clamp and lead/s on the haulage cord; and
4. Pull the haulage cord over the conductor or through the stirrup

Portable Earthing For Switchyards

Connection To Earth End Point

Earthing stubs shall be used for all earth end connections within medium/high voltage switchyards and these are generally installed on structures in the area where it is normally necessary to apply portable earths. It is important to ensure that the stub is not corroded and that it is securely mounted on the structure. Only use the CATU MT-815S clamps with earth stubs. At the earth end, the CATU MT-815S clamp can be applied with a CATU insulating stick or the CATU MT-815S application handle.

Portable Earthing Leads For Overhead Lines & Transmission

Connection to Earth End Point on Steel Tower Overhead Lines

For steel tower earthing systems, the tower itself is used as the earth point. CATU MT-847 surface penetrating clamps shall be used on painted or galvanised surfaces. When applying earth end clamps to a steel tower the clamps should be attached to a flat part of the tower structure and screwed up as tightly as practicable by hand.

Connection to Earth End Point On Wood Or Concrete Pole Overhead Lines

Pole earthing systems involves the use of both the pole earth and an independent temporary earth electrode (earth stake). The earth stake is to be positioned approximately 1.3m from the pole and driven 600mm into the ground then bonded to the pole earth using a standard portable earth lead with either CATU MT-815S clamps applied with a shotgun stick or MT-815S application handle

Portable Earthing For Switchgear

In general, indoor medium/high voltage switchgear is provided with manufacturers specific portable earthing systems. However, the dedicated earthing system provided maybe inadequate or non-functioning. The application of portable earthing systems in indoor switchgear situations is usually limited by physical clearances. The choice of MV-HV earthing system used will therefore be determined by the geometry of the switchgear involved and the practicality of applying the available portable earthing equipment within restricted spaces. Any of the earth systems covered in this procedure, when used with earth clamps approved for indoor use, can be implemented in indoor situations.

The Bridge Method is commonly used where the fault rating of the indoor switchgear is less than or equal to the 25 kA 0.5 second rating.

Portable Earthing - Bridge Method

Portable Earthing Using The Bridge Method

 

Connection To Earth End Point

Earthing stubs shall be used for all earth end connections and these are generally installed on structures in the area where it is normally necessary to apply portable earths. It is important to ensure that the stub is not corroded and that it is securely mounted on the structure. Only use the CATU MT-815S clamps with earth stubs. At the earth end, the CATU MT-815S clamp can be applied with a shotgun stick or the CATU MT-815S application handle.

Use Of The CATU MT815S Clamp On Medium & High Voltage Indoor Switchgear

Clamps can be applied to stirrups and conductors. In certain indoor switchgear situations, an ‘Earth Stub’ may have been installed on the bus bar or conductor to enable the application CATU MT-815S clamps.

Use Of The Pfisterer 360333333 Clamp On Indoor Medium & High Voltage Switchgear

Known as universal angle clamps these are applied to ball stubs using a CATU CM710 E application handle. Once the earth clamp is placed onto the apparatus to be earthed the application handle is removed.

Portable Earth Clamps

Portable Earth Clamps with Pfisterer 360333333

Portable Earthing Situations Line End Clamps Earth End Clamps Reference
Connection CATU Clamp Application Connection Clamp Application
Conductors In Substations Earthing Stirrup MT815S Shotgun Stick Earth Stub Screw Action Clamp MT815S MT 815S Application Handle Application of Portable Earthing In MV HV Switchyards
Conductor MT-701 Haulage & Release Cord, Sandbag, HV Operating Rod
Steel Tower Overhead Lines Conductor MT815S Shotgun Stick Tower Structure Surface Penetrating Clamp By Hand Application of Portable Earthing On Overhead Transmission Lines
Connection To Earth End Point On Steel Tower Overhead Lines
MT815E CATU CM-4130-E Application Stick
MT-701 Haulage & Release Cord, Sandbag, HV Operating Rod
Wood & Concrete Pole Overhead Lines Conductor MT815S Shotgun Stick Earth Stake Screw Action Clamp MT815S MT 815S Application Handle Application of Portable Earthing On Overhead Transmission Lines
Connection To Earth End Point On Wood Or Concrete Pole Overhead Lines
MT815E CATU CM-4130-E Application Stick
MT-701 Haulage & Release Cord, Sandbag, HV Operating Rod
Indoor Switch Gear Conductor MT815S Shotgun Stick Earth Stub Screw Action Clamp MT815S MT 815S Application Handle Application Of Portable Earthing On Indoor Switchgear
Ball Point Universal Angle Clamps CM710E Application Stick
Mobile Plant Earth Stub On Mobile Plant Chassis MT815S MT 815S Application Handle Earth Stub Screw Action Clamp MT815S MT 815S Application Handle Mobile Plant In The Vicinity Of High Voltage Conductors
Mobile Plant Chassis Or Boom Surface Penetrating Clamp By Hand Earth Stub Screw Action Clamp MT815S MT 815S Application Handle
Tower Structure Surface Penetrating Clamp By Hand
Earth Stake Screw Action Clamp MT815S MT 815S Application Handle

 

Screw Action Clamp – CATU MT815S Screw Action Clamp - CATU MT815S
Approved Rating 40kA/0.5 seconds
Use Line or Earth end connections for Earthing, Bonding & Bridging
Limitations of Use Round Conductor up to 44mm in diameter, Flat Conductor from 3mm to 40mm in thickness
Drawing Number STD-647175
Stockcode 3180437
Associated Equipment Shotgun Stick or Hand Application Tool
Screw Action Clamp – CATU MT815E Screw Action Clamp - CATU MT815E
Approved Rating 25kA/0.5 seconds
Use Line end connections for transmission line earthing
Limitation of Use Round Conductor up to 44mm in diameter
Drawing Number
Stockcode
Associated Equipment CATU CM-4130-E application stick
Universal Angle Clamp – Pfisterer 360 333 333 Universal Angle Clamp - Pfisterer 360 333 333
Approved Rating 40kA/0.5 seconds
Use Line end connections for Indoor Earthing
Limitations of Use Haymarket 11kV
Drawing Number
Stockcode Not Stocked
Associated Equipment CM 710 E application stick
Snap Action Line Clamp – CATU MT-701 Snap Action Line Clamp - CATU MT-701
Approved Rating 40kA/0.5 seconds
Use Line end earthing connections only
Limitations of Use Round Conductors 20 to 40mm diameter
Drawing Number STD-197006
Stockcode 986968 ea
986901 complete set with single leads
986893 complete set with twin leads
CATU CM 710 E Insulating Sticks CATU CM 710 E Insulating Sticks
Approved Rating Not applicable
Use Haymarket 11kV Indoor
Limitations of Use Must be used only with Pfisterer 360 333 333
Stockcode Not stocked
Associated Equipment Pfisterer 360 333 333 clamp
CATU CM 4130 E Insulating Sticks CATU CM 4130 E Insulating Sticks
Approved Rating Not applicable
Use Insulating stick for line end connections for transmission line earthing
Limitations of Use Must be used only with CATU MT815E clamps
Stockcode
Associated Equipment CATU MT815E clamps

 

Glossary

Term Definition
Earth Stake A steel rod driven into the ground to provide an earth point for portable earthing equipment
Earth Lead A yellow flexible cable that connects the conductors of equipment required to be earthed through clamps or other means to the general mass of the earth
Bridging The process of placing a conductor (or bridge) across a break in an electrical circuit (HV conductor, neutral or earthing system) in order to maintain electrical continuity
Fault Current Abnormally high current that flows due to partial or complete failure of insulation at one or more points
Earthing System A group of components that performs a short circuiting or earthing function
Earthing Equipment Any piece of equipment for the purpose of earthing, either individually or combination
Line End That part of an earthing set connected to conductors or other apparatus that may be energised
Earth End That part of an earthing set connected to the general mass of earth directly, or through an “earthed” piece of equipment e.g structure or earth grid
Trifurcating Plate An aluminium plate used to connect the earthing leads and provides a short circuiting point for the phases
Screw Action Clamp A clamp in which the mechanism of attachment to conductors is carried out by a positive screw thread
Snap Action Clamp A clamp by which attachment to the conductors is carried out by a spring operated mechanism
Haulage & Release Cord Associated with snap action clamps, enables the clamp to be hauled up and applied to the conductor to be earthed

Trifurcated Earthing System

Portable Earthing

Single Phase, Single Lead Earth System

Portable Earthing

Single Phase, Twin Lead Earth System

Portable Earthing

 

Substation Earthing

Thorne & Derrick International distribute ABB Furse and AN Wallis Earthing & Lightning Protection Systems for the protection and grounding of Medium, High & Extra High Voltage Substations – this includes copper earth tapes, earth rods, copper earthing plates, clamps and ancillary items for 33kV, 66kV, 132kV and 275kV substations. For more information please see substation earthing.

AN Wallis Earth Tapes Earth Bars Copper

AN Wallis – Copper Earth Tapes | Bars | Clamps | Rods

Thorne & Derrick Specialist Electrical DistributorThorne & Derrick

LV ♦ MV ♦ HV

T&D distribute the most extensive range of LV, MV & HV Cable Jointing, Terminating, Installation & Cable Pulling Equipment – we service UK and international clients working on underground cables, overhead lines, substation earthing and electrical construction at LV, 11kV, 33kV and EHV transmission and distribution voltages.

  • Key Products: MV-HV Cable Joints & Terminations, Cable Cleats, Duct Seals, Cable Transits, Underground Cable Protection, Cable Jointing Tools, Feeder Pillars, Cable Ducting, Earthing & Lightning Protection, Electrical Safety, Cable Glands, Arc Flash Protection & Fusegear.
  • Distributors for: 3M, ABB, Alroc, Band-It, Catu, Cembre, Centriforce, CMP, Elastimold, Ellis Patents, Emtelle, Furse, Lucy Zodion, Nexans Euromold, Pfisterer, Polypipe, Prysmian, Roxtec.

The Alroc range of jointing tools are extensively used to enable the installation of MV HV Joints, Terminations & Connectors including Prysmian, Elastimold, 3M, Pfisterer and Nexans Euromold.

Further Reading