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ENR-LHQ Series Cable Sheath Protector

I.Overview

35kV large-section power cables and 66kV,110kV and above voltage level power cables are mostly single-core cables.The metal sheath of the cable is interconnected and grounded at one end of the three phases,while the other end is ungrounded.When lightning waves or internal overvoltages flow along the cable core,a high impact overvoltage will appear at the ungrounded end of the cable metal sheath.Alternatively,when a system short-circuit fault current flows through the cable core,a high power frequency induced overvoltage will also appear at the ungrounded end of the sheath.The aforementioned overvoltages may break down the insulation of the cable outer sheath,causing a multi-point grounding fault in the cable metal sheath,which generates induced currents.As a result,the cable shielding layer will heat up,consuming a large amount of electrical energy and affecting the normal operation of the line.According to the power industry standard DL/T401-2002"Guide for the Selection of High-Voltage Power Cables,"a cable sheath protector must be used to limit the induced voltage and fault overvoltage on the metal sheath(or metal armor)of power cables.

Typically,to limit the induced voltage and fault overvoltage on the metal sheath of power cables and avoid forming circulating currents in the sheath,one end of the cable metal sheath is directly grounded,while the other end must be grounded through a protector.If the line is long,the cable sheath should also be divided into three segments(or multiples of three segments)with insulation between them,and the sheath at the segment junctions should be cross-connected and grounded through protectors.

In response to the operational characteristics of power system cables,Baoding Enol Electric has developed and produced the ENR-LHQ series cable sheath protectors,which can be widely used in single-core power cable lines to protect the metal sheath of the cable from various overvoltage hazards.To better meet market demands and facilitate on-site installation and use by customers,our company has further developed several types of sheath grounding devices,including direct grounding boxes,protective grounding boxes,and cross-connected protective grounding boxes.Currently,various cable sheath grounding devices produced by our company have been widely used in power systems nationwide,gaining valuable operational experience.

II.Product Working Principle and Features

The cable sheath protector is installed between the metal sheath of the cable and the ground(see Figure 1).Under normal conditions,the current passing through the protector is minimal,at the microampere level;when overvoltage occurs on the cable sheath,the protector quickly activates to discharge the charge on the sheath,ensuring the safe operation of the cable.

The protector utilizes ZnO varistors as protective elements,with no series gap,featuring an excellent nonlinear voltage-current characteristic curve and superior protective performance.It not only possesses the advantages of porcelain-housed metal oxide arresters but also boasts excellent electrical insulation properties,high dielectric strength,resistance to tracking and erosion,heat and cold resistance,aging resistance,explosion-proof capabilities,as well as good chemical stability,hydrophobicity,and sealing performance.

Figure 1:Schematic diagram of protector wiring

3、、、Product Model Description

ENR-LHQJS-6~500kV cable sheath protector(composite jacket,with discharge counter)

ENR-LHQ-6-500kV cable sheath protector(composite jacket,without discharge counter)

4、、、Performance parameters of protector

There are eight voltage levels ranging from 6 to 500kV in specifications,and their technical parameters are shown in the following electrical characteristic table.

Table 1:Electrical Characteristics of Cable Sheath Protectors

Figure 1:Schematic diagram of protector wiring

3、、、Product Model Description

ENR-LHQJS-6~500kV cable sheath protector(composite jacket,with discharge counter)

ENR-LHQ-6-500kV cable sheath protector(composite jacket,without discharge counter)

4、、、Performance parameters of protector

There are eight voltage levels ranging from 6 to 500kV in specifications,and their technical parameters are shown in the following electrical characteristic table.

Table 1:Electrical Characteristics of Cable Sheath Protectors

Note:The*marked values indicate residual voltage under a lightning impulse current of 16kA.

V.Usage Conditions

1.Ambient temperature range:-45℃to+55℃;

2.Altitude not exceeding 4500m;custom solutions available for altitudes beyond 4500m based on actual conditions;

3.Power frequency:58～62Hz(for 60Hz systems),48～52Hz(for 50Hz systems);installation sites must be free from chemically corrosive gases and explosive dust in the air.

4.The long-term applied power frequency voltage must not exceed the protector's continuous operating voltage;for products with gaps,the short-term power frequency voltage rise at the installation point must not exceed the protector's rated voltage.

5.For long-term use under abnormal conditions,the protector needs to be specially manufactured.Please specify when placing an order.

VI.Dimensions and Installation Specifications

VII.Usage Instructions

1.The ENR-LHQ series cable sheath protector is a specialized device designed to safeguard cable sheaths,preventing damage from lightning strikes and induced overvoltages.

2.The protector is connected in parallel between the high-voltage cable sheath and the ground,as shown in Figure 1.It is put into operation by connecting it to the cable sheath using M10 mounting bolts.During installation,the tensile force on the lead wire at the high-voltage outlet end should not exceed 147N.The insulation level of the connecting wire should not be lower than that of the protected cable's outer sheath,and the connection loop should be as short as possible.The device must be reliably grounded.

3.This product cannot continuously withstand power frequency overvoltages beyond its rated capacity.The power frequency withstand capabilities for specific models are listed in Table 1.

4.As an optional feature,this product can be equipped with an operation counter.Users may select this feature as needed and should specify it when placing an order.

5、、、The appearance and installation dimensions of the protector are subject to the actual product.

6.After the protector has been in operation for one year,preventive tests should be conducted,including the following items:

(1)DC 1mA voltage measurement:

Apply a DC voltage(with ripple not exceeding±1.5%)across the protector.When the current through the protector stabilizes at 1mA,read the voltage value.This value must not be less than the DC reference voltage specified in Table 1.

(2)Insulation resistance test:

Use a 2500V megger to measure the insulation resistance of the protector.There is no specified requirement for the insulation resistance value,but the results obtained from each measurement should be consistent.There should be no open circuit,poor contact,or short circuit phenomena.

8.Ordering Instructions

Please provide the following parameters when ordering cable sheath protectors:

1.The rated voltage level of the power cable,or specific performance parameter requirements for the cable sheath protector;

2.Whether the protector is to be installed indoors(such as in grounding boxes or switchgear)or outdoors;

3.Order quantity and delivery time;

Any special requirements should be specified at the time of ordering.

Our company will persistently strive to improve product performance,and version changes may occur without prior notice.