Introduction to High Voltage



What is Voltage and High Voltage?

    •   Voltage is the Electric Potential difference between two points.
    •   If the voltage is on or above 1000 V ( 1 kV), we called it High Voltage.


Types of High Voltages

Alternating Current (AC)

o            High Voltages High Voltage AC (HVAC): 1000 V (1 kV) and up to 1,000,000 (1000 kV)

o            Ultra-High Voltage AC (UHVAC): 1,000,000 (1,000 kV)

        Direct Current (DC)

o             High Voltages High Voltage DC (HVDC): 1000 V (1 kV) and up to 1,000,000 (1000 kV)

    (Some classifications use 1.5 kV instead of 1 kV)

o            Ultra-High Voltage DC (UHVDC): 1,000,000 (1,000 kV) and above

       Challenges Associated with High Voltage (HV) Systems:

1.      Infrastructure to Handle High Voltages

·         HV systems require specialized infrastructure, such as insulated transmission lines, substations, and switchgear to manage high voltage levels safely.

·         The construction and maintenance of these facilities demand high costs and expertise.

2.      Required Specific Equipment

·         High voltage applications need specialized transformers, circuit breakers, insulators, and conductors designed to withstand extreme voltages.

·         Testing and maintenance equipment must also be suitable for HV conditions.

3.      Protection and Monitoring

·         High voltages pose a higher risk of faults (such as insulation failure, arcing, and corona discharge).

·         Advanced protection relays, surge arresters, and SCADA-based monitoring systems are required to detect and mitigate faults.

4.      Safety

·         HV systems are extremely dangerous, requiring strict safety measures, including proper grounding, isolation, and personal protective equipment (PPE).

·         Workers must be trained in HV safety protocols to avoid electrical hazards like shocks and arc flash incidents.

5.      Clearance

·         Adequate clearance distances must be maintained for HV power lines and equipment to prevent flashover and unintended contact.

·         Right-of-way management is necessary to avoid obstructions (e.g., trees, buildings) near HV lines.

High Voltage Equipment

High Voltage Transformers (HV Transformers)

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High-voltage (HV) Transformers are critical components in electrical power systems. They are used to raise or lower voltage levels for efficient transmission and distribution. They ensure that power is transmitted over long distances with minimal losses and safely delivered to consumers.

Types of High Voltage Transformers

  1. Power Transformers
    • Used in transmission networks to step up voltage for long-distance transmission and step-down voltage for distribution.
    • Operates at voltages above 33 kV and has high power ratings (up to 1000 MVA).
  2. Instrument Transformers
    • Current Transformers (CTs): Reduce high currents to measurable levels for meters and protection systems.
    • Voltage Transformers (VTs) or Potential Transformers (PTs): Step down high voltages for safe measurement and relay operation.
  3. Distribution Transformers
    • Steps down voltage for local distribution to homes and industries (e.g., from 11 kV to 400V).
    • Lower power ratings compared to power transformers (up to 5 MVA).
  4. Autotransformers
    • Uses a single winding to transfer power with a common section for both primary and secondary.
    • More compact and efficient than conventional transformers but with limited isolation.
  5. Phase-Shifting Transformers (PSTs)
    • Controls power flow between different grid sections by adjusting phase angles.
    • Helps in load balancing and preventing overloading in transmission networks.
  6. HVDC Converter Transformers
    • Used in high-voltage direct current (HVDC) systems to convert AC to DC and vice versa.
    • Designed to handle high voltages and harmonic stresses

High Voltage Equipment: Bushings & Insulators

What are HV Bushings?

Bushings are insulating components that allow electrical conductors to pass through grounded barriers (e.g., transformer tanks, circuit breakers, switchgear) without causing short circuits.

Types of HV Bushings

  1. Oil-Impregnated Paper (OIP) Bushings
    • Uses paper impregnated with insulating oil for electrical insulation.
    • Commonly used in power transformers and circuit breakers.
    • Requires regular oil maintenance and monitoring.
  2. Resin-Impregnated Paper (RIP) Bushings
    • Insulation is achieved using paper impregnated with epoxy resin.
    • No oil, so it has better environmental and fire safety.
    • More durable and maintenance-free compared to OIP bushings.
  3. Resin-Bonded Paper (RBP) Bushings
    • Similar to RIP but uses a different resin bonding technique.
    • Used in medium voltage applications.
  4. Capacitive Graded Bushings
    • Contains multiple capacitive layers to distribute voltage evenly, reducing electrical stress.
    • Used in EHV and UHV applications (400 kV and above).

What are HV Insulators?

HV insulators prevent current leakage by supporting conductors and isolating them from the ground or structures.

Types of HV Insulators



Types Based on Application

  • Pin Insulators → Used for lower voltage distribution lines.
  • Suspension Insulators → Used in HV transmission lines (above 33 kV).
  • Strain Insulators → Supports long spans and mechanical loads in transmission systems.
  • Post Insulators → Used in substations and switchgear.

 

 

High Voltage Circuit Breakers (HVCBs)

High Voltage Circuit Breakers (HVCBs) are essential components in power systems for interrupting high voltage electrical currents under normal and fault conditions. They protect electrical grids by isolating faulty sections, preventing damage to equipment, and ensuring system stability.

Types of High Voltage Circuit Breakers

  1. Air Circuit Breaker (ACB)
    • Uses compressed air to extinguish the arc.
    • Mainly used in medium voltage applications but also found in some HV systems.
    • Requires frequent maintenance due to arc chutes and moving parts.
  2. Oil Circuit Breaker (OCB)
    • Uses insulating oil as both an arc-extinguishing medium and an insulator.
    • The oil absorbs the arc energy, vaporizing and creating a high-pressure bubble to extinguish the arc.
    • Requires regular oil replacement and maintenance to remove carbon deposits.
  3. SF₆ Circuit Breaker (Sulfur Hexafluoride)
    • Uses SF₆ gas as an insulating and arc-quenching medium.
    • Offers excellent dielectric strength, fast operation, and minimal maintenance.
    • Widely used in extra high voltage (EHV) and ultra-high voltage (UHV) systems.
  4. Vacuum Circuit Breaker (VCB)
    • Uses vacuum as the arc-extinguishing medium.
    • The arc is extinguished quickly due to the absence of ionized particles.
    • Suitable for medium voltage but limited for HV applications.
  5. Hybrid Circuit Breakers
    • Combines the advantages of SF₆ and vacuum technologies.
    • Faster operation and reduced environmental impact.
    • Used in smart grid and high-speed switching applications.