Sheath Voltage Limiters | Ensto Varisil HC 4kV – 14.4kV Cable Sheaths

Sheath Voltage Limiters | Ensto Varisil HC 4kV – 14.4kV Cable Sheaths

Sheath Voltage Limiters | Ensto Varisil HC 4kV – 14.4kV Cable Sheaths

Sheath Voltage Limiters

Ensto Varisil HC are sheath voltage limiters suitable for 4kV – 14.4kV cable sheaths for connection to single point bonded sections dedicated to the protection of DC powered equipment in substations or on trains. HC surge arresters are designed for overvoltage protection of Power Transmission & Distribution underground cable sheaths.

The design of Ensto Varisil HC sheath voltage limiters are in accordance with CIGRE recommendations and IEC 60099-4 principles.

  • Part Number : ENSTO 7250041
  • Sheath Voltage Limiters SVL : ENSTO VARISIL HC
  • Rated voltage Ur : 1 kV up to 18 kV
  • Nominal discharge current : 10 kA
  • High current impulse withstand : 65 kA
  • Long duration current impulse withstand : 150 A
  • High resistance to climatic stresses
  • Optimized electrical performance
  • Long creepage distance
  • Maintenance-free Sheath Voltage Limiters SVL
Ensto Varisil HC 4kV – 14.4kV

Ensto Varisil HC 4kV – 14.4kV

Varisil HC Sheath Voltage Limiter

Technical Specification


Max. operating temperature: +70 °C
Ambient temperature :  -50°C to +50°C
Humidity: 100% at 25 °C (max)
Storage temperature: -50 … +80 °C


Electrical Values

Operating voltage: 4 to 14,4kV
Rated discharge current: 10 kA
Dry lightning impulse withstand voltage: ≥ 95 kV
Wet power frequency withstand voltage: ≥ 35 kV



Tightening torque: 30 N.m
Max. continuous load: 1200 N
Highest permitted load in use: 1.5 kN



Rated voltage: 5 … 18 kV
Degree of protection: IP67
Rated frequency: 50-60Hz
Fire resistance class: HL3-R23 / EN 45545-2


Short-circuit Characteristics

Rated short time withstand current: 31,5kA rms / 0,2


Sheath Voltage Limiters SVL Specification HC05 HC10 HC12 HC15 HC18
Rated voltage Ur 5 10 12 15 18
Continuous operating voltage Uc 4 8 9.6 12 14.4
Nominal discharge current In (kA 8/20) 10 10 10 10 10
High current impulse withstand (kA 4/10) 65 65 65 65 65
Long duration current withstand (A 2000 µs) 150 150 150 150 150
Short circuit withstand (kA eff/0,2s) 31.5 31.5 31.5 31.5 31.5
Ensto Varisil HC Sheath Voltage Limiters Dimensions

Ensto Varisil HC Sheath Voltage Limiters Dimensions


Dimensions HC05 HC10 HC12 HC15 HC18
Ho (mm) 195 195 195 195 195
H1 (mm) 255 255 255 255 255
H2 (mm) 290 290 290 290 290
Poids version NO (kg)
Weight No version (kg)
1.4 1.6 1.7 1.8 1.9

Ensto Varisil HC

  1. Stainless steel top stud
  2. Securing nut
  3. Stainless steel top cap
  4. Aluminium electrode
  5. Metal oxide varistor
  6. Synthetic tape
  7. Composite wrappings
  8. Silicone rubber housing
  9. Stainless steel bottom cap
  10. Stainless bottom stud

Selecting the correct Sheath Voltage Limiter

The choice of the Sheath Voltage Limiters must be made according to the application :

  • RNL HC range for the mounting in cabinets with cross bonding
  • VARISI HC for mounting at ends of single point bonded sections

The selection of the appropriate Sheath Voltage Limiters within the range is based on two considerations having opposite impacts :

  • The 1.2/50 lighting impulse withstand level of the sheath, which depends on the external insulation of the cable tends to minimize the required protective level
  • The voltage induced at the connecting point of device in case of short circuit on the main conductor, which depends on the short circuit power and on the length of the cable to be protected, leads to maximize the rated voltage

A protective margin greater than 20% is recommended between the protective level of the surge arrester (Up) and the lightning impulse withstand level of the sheath (Uw).

On the other hand, the level/time values (Usc/T) of the voltage induced on the sheath in case of short circuit must be below the minimum voltage vs time characteristic curve of the surge arrester.

Whenever several references meet both requirements, the final choice will be made by the user with respect to operation requirements and priorities.

Basically, the surge arrester with lower rated voltage will provide improved protection whereas the surge arrester with higher rated voltage will better withstand short circuit stresses. Any surge arrester in-between will be a compromise.

Should no reference fulfil both requirements, the protection should be achieved at shorter intervals so as to allow the use of a surge arrester having a lower rated voltage.

Example : Cable features:

  • Single point bonded cable
  • Uw = 55 kV
  • usc = 300 V/kA/km
  • sc = 31.5 kA / T = 1 s
  • L = 1.8 km

Selection of Sheath Voltage Limiter :

  2. 20% protective margin : Up < Ut/1.2 thus Up < 46 kV
  3. Voltage withstand under short circuit conditions : Ucs = usc x lcc x L = 17 kV and U (T = 1s) = 1.2 x Ur gives 1.2 x Ur > 17 so that Ur > 14.2 kV

Here, the calculation leads to Ensto VARISIL™ HC 15 model.

➡ See also: Surge Diverters MV HV

Sheath Voltage Limiters

Sheath Voltage Limiters MV HV – Medium & High Voltage Cables & Networks

Data Sheets