Compact Circuit Breaker (HT Panel 11KV)

About Compact Circuit Breaker (HT Panel 11KV)

VCB panels are essential components in electrical power distribution systems, providing safe and efficient protection against faults in high-voltage circuits. These panels use vacuum circuit breakers (VCBs) to interrupt current flow and protect electrical equipment from damage. HT (High Tension) VCB (Vacuum Circuit Breaker) panels are used in medium-voltage power distribution (typically from 3.3kV to 36kV) for switching and protection. As per RBs Letter, CPWD General specifications for Electrical Works Part-IV Substation2013" are comprehensive may be adopted over Indian Railways for sub-station items. In this specification section 2 is related to High Voltage Panel. A railway 11kV substation generally uses two transformers of the same capacity-one in operation and the other on standby. The electricity supply from the board is received through an HT VCB panel, which also provides protection for the HT side of these transformers. Figure 1: Schematic of power supply arrangement in a 11kV Substation 1.3 CLASSIFICATION OF HT VCB PANEL The types of HT VCB panels are classified based on their application, design, and operational features. Here are the main types: Based on Installation Location Indoor VCB Panel Installed inside substations or switchgear rooms, protected from environmental factors. Outdoor VCB Panel Designed for outdoor use with weatherproof enclosures. CAMTECH/E/2024-25/EP-05/HT VCB/1.0 Booklet on HT Vacuum Circuit Breaker Panels 4 Based on Operation Mechanism Fixed Type VCB Panel The breaker is fixed inside the panel and cannot be removed for maintenance easily. Draw-out Type VCB Panel The breaker can be removed from the panel, making maintenance easier. Based on Voltage Rating 11kV VCB Panel Common for industrial and commercial distribution systems. 22kV VCB Panel Used for higher voltage distribution networks. 33kV VCB Panel Typically found in transmission and large industrial plants. Based on Application Single Busbar VCB Panel Standard configuration for power distribution. Double Busbar VCB Panel Provides redundancy and flexibility in switching. Feeder Protection/ Ring Main Unit (RMU) VCB Panel Used in distribution networks for load switching or creating ring main system between multiple sub-station for incoming supply. CAMTECH/E/2024-25/EP-05/HT VCB/1.0 Booklet on HT Vacuum Circuit Breaker Panels 5 CHAPTER 2 CONSTRUCTIONAL FEATURES VCB Panels shall be metal clad, indoor type, motor operated ON/OFF from front, Vertical/Horizontal isolation, horizontal draw out type truck of robust construction, fully Interlocked and extendable on both sides. Separately earthed compartments shall be provided for circuit breakers, bus bars, relay & instruments, CT & PT and cable boxes, fully and effectively segregating these from one another so that fault in any one compartment do not cause damage to equipment in other compartment. The housing shall be of bolted construction to ensure compact and rigid structure, presenting a neat and pleasing appearance. The sheet steel used should not be less than 2 mm thick. 2.1 GENERAL ARRANGEMENTS The circuit breaker panels shall be complete with the following: (a) Racking in / Racking out mechanism. (b) Isolating plugs and sockets. (c) Mechanical inter-locks and safety shutters. (d) Mechanical ON/OFF indicator. (e) Minimum of 4 NO and 4 NC Auxiliary contacts directly operated by the circuit breaker. Additional NO & NC contacts can be provided with auxiliary contractors. (f) Anti-condensation space heaters suitable for operation on 240V, 50 Hz A.C. for each panel wherever specified. (g) Suitable tripping arrangement. (h) Mechanical counter to assess the total number of operations of the breaker (if asked for specifically). Figure 2: Typical General Arrangement of HT VCB Panels CAMTECH/E/2024-25/EP-05/HT VCB/1.0 Booklet on HT Vacuum Circuit Breaker Panels 6 Mechanical Interlocks Mechanical interlocks are physical mechanisms designed to prevent unsafe operations by ensuring the correct sequence of actions in HT VCB (High Tension Vacuum Circuit Breaker) panels. These interlocks help avoid dangerous conditions like simultaneous operation of breakers or access to live parts. Common Types of Mechanical Interlocks: Breaker Interlock: Prevents the VCB from being closed when the panel door is open, ensuring operator safety. Truck Interlock (for Drawout Type VCBs): Prevents racking in/out of the breaker unless it is in the OFF position. Earthing Switch Interlock: Ensures the breaker is OFF before the earthing switch can be engaged. Busbar Interlock: Prevents two different power sources from being connected simultaneously, avoiding back-feeding and faults. Safety Shutters Safety shutters are movable barriers in VCB panels that automatically cover live busbar contacts when the breaker is withdrawn (in drawout-type panels). Function of Safety Shutters: Prevents accidental contact with live busbars when the breaker is removed. Operates automatically (opens when the breaker is inserted, closes when it is removed). Enhances electrical safety during maintenance 2.2 COMPONENT OF INDOOR VCB PANEL Figure 3: Various Components of 11 kV VCB Panels CAMTECH/E/2024-25/EP-05/HT VCB/1.0 Booklet on HT Vacuum Circuit Breaker Panels 7 An Indoor VCB Panel consists of several key components that ensure safe and efficient operation in medium-voltage power distribution. Below are the main parts of an Indoor VCB panel: Vacuum Circuit Breaker (VCB) The Vacuum Circuit Breaker (VCB) is the core switching device responsible for making and breaking the circuit under normal and fault conditions. It operates within a vacuum chamber, where the absence of air and other gases ensures rapid arc extinction. The VCB consists of: 2.2.1.1 Fixed & Moving Contacts: When separated, an arc forms, but it is quickly extinguished due to the vacuum environment. 2.2.1.2 Operating Mechanism: Uses spring-charged manual or motorized systems to open and close the breaker. 2.2.1.3 Interrupter Chamber: Encapsulates the vacuum where the contact separation occurs, ensuring safe operation. 2.2.1.4 Insulation Housing: Prevents electrical leakage and protects internal components. Figure 4: VCB and their components Figure 5: Vacuum Interrupter Unit CAMTECH/E/2024-25/EP-05/HT VCB/1.0 Booklet on HT Vacuum Circuit Breaker Panels 8 Current Transformer Double wound resin cast current transformers of approved ratio burden 15 VA, accuracy class 5P-10 for protection and class 1.0 for metering, ON/OFF indications. Figure 6: Resin Cast Type Current Transformer (CTs) 2.2.2.1 General Requirements Accommodation shall be provided in the circuit breaker panel to mount one set of three numbers dual core dual ratio CTs for metering and protection purposes. Access to the CTs for cleaning, testing or changing shall be from the front, back or top of the panel. 2.2.2.2 Rating Dual core & dual ratio CTs of suitable burden (but not less than 15 VA) shall be preferred with 5 Amps secondary. CT ratio shall be compatible with the loading pattern on HV side. The CTs shall conform to relevant Indian Standards. The design and construction shall be robust to withstand thermal and dynamic stresses during short circuits. Secondary terminals of CTs shall be brought out suitably to a terminal block which will be easily accessible for testing and terminal connections. The protection CTs shall be of accuracy class 5P10. The metering CTs shall conform to the metering ratio and accuracy class 0.5 for incomer and class 1 for outgoing panels. Potential Transformers A Potential Transformer (PT) (also called a Voltage Transformer, VT) is primarily used for voltage measurement, protection, and control in high-voltage systems. Its main applications include: Figure 7: Resin Cast type PT in VCB panels CAMTECH/E/2024-25/EP-05/HT VCB/1.0 Booklet on HT Vacuum Circuit Breaker Panels 9 2.2.3.1 Metering & Measurement PTs step down high voltage (e.g., 11kV, 33kV) to a safer, measurable level (e.g., 110V) for energy meters, voltmeters, and other measuring instruments. Ensures accurate voltage readings for system monitoring. 2.2.3.2 Protection System Provides input signals to protective relays (e.g., overvoltage, undervoltage, and distance relays) for fault detection and tripping if voltage abnormalities occur. It works with Relays like Numerical Relays, Distance Relays, and Voltage-Based Protection Relays. 2.2.3.3 SCADA & Remote Monitoring PT output is used in SCADA (Supervisory Control and Data Acquisition) systems for realtime voltage monitoring and remote control. A voltage transformer of 100 VA, 3x11000/110 volts, resin cast potential transformer of accuracy class 3 with protective fuses for protection. A voltage transformer of burden not less than 100 VA. The accuracy class for the VT shall be class 0.5 for incomer and class 1 for outgoing panels. The transformer shall be of cast epoxy resin construction. It shall be fixed/withdrawable type. HRC fuses/ MCBs shall be provided on both HV and LV sides. Protective Relay The Relays shall be microprocessor based numerical relays with O/L, E/F and S/C protection Tripping relay shall be used for tripping signal to the Shunt Trip Coil of Circuit Breaker operating on 24 V/ 30 V DC supply / Power pack / 110 V VT supply. 2.2.4.1 Various Relays Main Protection Relay - Overcurrent and earth fault relay - Restricted earth fault relay - Master Trip Relay Auxiliary Protection Relay - Auxiliary Alarm Relay (For OTI, WTI and Buchholz Relay) - Auxiliary Trip Relay (For OTI, WTI and Buchholz Relay) Figure 8: Various Protective Relays CAMTECH/E/2024-25/EP-05/HT VCB/1.0 Booklet on HT Vacuum Circuit Breaker Panels 10 Figure 9: Connection of Primary and Auxiliary Protective Relays 2.2.4.2 Relays setting Over current Relays shall have adjustable setting for current from 50% to 200% and earth fault from 10% to 40% or 20% to 80%. These should be of manual reset type. All relays shall have a LED indicator, which will indicate operation for each function. It shall be possible to reset it only by manual operation. The number and types of relays shall be as specified. Note: 24V/ 30V DC shall be provided through 2 No. SMF batteries of 12/ 15 volts of minimum 26 AH capacity with a battery charger as per recommendation of the manufacturer both for protection as well as indications. Alternatively, Power Pack converters fed through PT/ 230V externally could be provided with 2 Nos., 12/ 15-volt, 7 AH SMF batteries (Power pack with condenser/ capacitor backup are also available which do not need batteries, these should not be used) for tripping. In cases where tripping is fed through PT, VA burden of PT shall be suitably increased (say 200 VA) as recommended by the manufacturer depending upon the number of panels and connected controls. In addition, external 24 volt / 30-volt DC supply shall be provided for indications etc. through 2 No. SMF batteries of 12/ 15 volts of minimum 26 AH capacity with a battery charger as per recommendation of the manufacturer

Advanced High Voltage Protection

This HT panel uses compact circuit breaker technology to safeguard medium and high voltage electrical lines. Suited for power ratings up to 500MVA and rated voltages of 11KV, 22KV, and 33KV, it handles the demands of modern electrical grids efficiently while protecting equipment from overcurrents and faults.


Durable Construction for Harsh Environments

Manufactured with cold rolled and CRCA steel, aluminium conductors, and a stainless steel cover, the panel resists corrosion and mechanical stress. The IP54/IP67 rating ensures reliable operation in challenging industrial and outdoor environments, with a powder-coated finish offering added protection and sleek appearance.


User-Friendly Digital Monitoring

Equipped with a digital display and RS 485 connectivity, the panel provides clear, real-time data, supporting effective monitoring and control. These features simplify diagnostics and help technicians ensure optimal performance and system reliability around the clock.