KYN28A-12 Metal-Clad Withdrawable Medium Voltage Switchgear (Metering Cabinet)

1. Product Overview

KYN28A-12 metering cabinet is a special type of 12kV indoor armored withdrawable central switchgear, independently designed for high-voltage electric energy measurement and voltage signal sampling in 10kV power distribution systems. It is generally arranged after the incoming cabinet on the main busbar side, working together with incoming cabinets, outgoing cabinets and lightning arrester cabinets to form a complete medium-voltage power distribution system.

Different from incoming and feeder cabinets, its core design objective is accurate, legal metering of grid power consumption and real-time voltage sampling for protection and monitoring systems. It adopts the same four-compartment fully isolated metal partition structure as standard KYN28A-12 switchgear, with IP4X protection grade, complete five-prevention mechanical and electrical interlocks, and can be widely applied in industrial power plants, commercial complexes, residential substations, photovoltaic power stations and other medium-voltage power supply projects for domestic and overseas power grid bidding.

2. Main Internal Equipment Configuration

Primary Circuit Components

Main Busbar & Branch Copper Busbars

Insulated TMY copper busbars connect the metering cabinet to the front incoming cabinet and rear feeder cabinets, transmitting 10kV three-phase high voltage to the primary side of measuring transformers.

Voltage Transformer (PT)

Three-phase voltage transformers are connected in parallel across the three-phase main busbar. They convert high 10kV primary voltage into standard low secondary voltage signals, which are supplied to energy meters, protection relays and power monitoring devices for voltage measurement and system voltage monitoring.

Metering Current Transformer (CT)

High-precision class 0.2S current transformers are installed in series on each phase busbar. They step down large primary load current into standard secondary current signals for accurate electric energy calculation.

High-Voltage Fuse for PT Protection

Fuses are matched at the primary side of voltage transformers. When short-circuit or overload faults occur inside PT, the fuse will blow instantly to isolate the faulty transformer and protect the whole busbar system.

Earthing Switch

Mounted inside the cable compartment for safe grounding and residual charge discharge during cabinet maintenance, interlocked with cabinet door and transformer trolley.

High-Voltage Live Display Sensors

Inductive sensors fitted on primary busbars to detect live status and send warning signals to the cabinet door indicator.

Secondary Metering & Control Components

High-precision Multifunctional Energy Meter

The core metering device, which receives current signals from CT and voltage signals from PT to calculate active power, reactive power, electricity consumption, power factor and other grid data for grid settlement.

Secondary Terminal Block & Metering Wiring Compartment

Special independent wiring area for CT/PT secondary loop wiring, with sealed wiring design to prevent unauthorized tampering, meeting power grid metering anti-theft requirements.

Signal Transmission Module

Upload metering data, busbar voltage and load parameters to the central power monitoring system via RS485 communication.

Fault Indicator & Control Buttons

Display bus live status, PT fuse breakage alarm signals and equipment abnormal status on the front instrument panel.

Cabinet Safety Structure

Independent bus compartment, transformer trolley compartment, cable compartment and secondary instrument compartment separated by metal arc-proof partitions.

Top pressure relief channel to release high-temperature arc gas in case of short-circuit faults.

Full set of five-prevention interlock mechanism to avoid misoperation.

3. Working Principle

3.1 Primary Power & Signal Sampling Principle

Three-phase 10kV high voltage is transmitted from the main busbar into the metering cabinet.

Voltage sampling: PT parallel-connected on A/B/C three phases converts 10kV high voltage into 100V standard secondary voltage.

Current sampling: Series CT converts high primary load current into 5A or 1A secondary standard current.

The PT and CT secondary signals are transmitted through dedicated metering secondary cables to the multifunctional energy meter, forming the complete sampling loop for electric energy measurement.

PT primary side fuses provide short-circuit protection for voltage transformers. Once internal PT short-circuit occurs, the fuse melts to cut off the primary circuit and avoid busbar short-circuit accidents.

3.2 Electric Energy Metering Principle

The multifunctional energy meter calculates power consumption based on synchronous voltage and current signals collected from PT and CT:

Multiply real-time voltage and current to obtain instantaneous power;

Integrate power over time to accumulate total active and reactive electricity consumption;

Automatically record forward/reverse power, peak/off-peak power, power factor and harmonic data;

Store historical metering data locally and support remote data upload for grid billing and settlement.

The secondary metering circuit adopts closed wiring design. All secondary wiring terminals are sealed to prevent man-made signal modification, which complies with international grid metering anti-cheating standards.

3.3 Voltage Monitoring & Auxiliary Protection Principle

The PT secondary voltage signal is also transmitted to the microcomputer protection device of the whole high-voltage system. The protection unit judges system abnormal conditions such as overvoltage, undervoltage and three-phase voltage unbalance, and sends alarm or tripping signals to relevant circuit breakers to maintain grid voltage stability.

3.4 Safety Interlock & Maintenance Principle

The cabinet is equipped with complete five-prevention interlock:

The PT/CT trolley cannot be pushed into the working position when the earthing switch is closed;

The earthing switch can only be closed after the trolley is withdrawn to the test position and the primary loop is fully powered off;

The cabinet door cannot be opened when the trolley is in working position with live busbar;

The PT fuse cannot be replaced when the primary busbar is electrified.

During maintenance, the trolley is pulled out, the earthing switch is closed to discharge residual high-voltage charge, creating a zero-voltage safe working environment for metering equipment inspection and meter replacement.

3. Grounding Safety Principle

The cabinet shell, metal partitions, PT/CT supports and earthing switch are all reliably connected to the station’s overall grounding grid. If insulation failure causes cabinet leakage, leakage current will be quickly led into underground grounding steel to prevent electric shock accidents for maintenance personnel.

4. Core Functions of KYN28A-12 Metering Cabinet

High-precision Grid Electric Energy Measurement

Match class 0.2S high-precision metering CT and PT to realize legal, accurate power consumption measurement for grid settlement, meeting the metering standards of power supply authorities worldwide.

System Three-phase Voltage Sampling & Monitoring

Continuously collect busbar voltage signals to support system overvoltage, undervoltage and three-phase unbalance monitoring, providing data basis for system protection logic.

PT Short-circuit Fault Isolation & Protection

Built-in primary high-voltage fuses cut off faulty voltage transformers rapidly to avoid busbar short-circuit and large-area power failure.

Isolated Anti-tampering Metering Loop

Independent sealed secondary metering wiring compartment prevents unauthorized modification of metering signals to guarantee measurement fairness.

Real-time Metering Data Upload & Remote Reading

Support RS485 communication to upload electricity consumption, voltage and power factor data to intelligent power monitoring background, realizing remote automatic meter reading for unattended distribution rooms.

Full Safety Protection Against Arc & Misoperation

Arc-proof separated compartments, top pressure relief device and five-prevention interlock system greatly reduce safety risks during equipment operation and maintenance.

5. Key Technical Parameters

Rated voltage: 12kV

Rated frequency: 50Hz / 60Hz (customizable for overseas markets)

Main busbar rated current: 630A, 1250A

Rated short-time withstand current: 20kA, 25kA, 31.5kA

Protection grade of cabinet: IP4X

Accuracy class of metering CT: 0.2S

Accuracy class of metering PT: 0.2

Operating ambient temperature: -10℃ ~ +40℃

Application environment: Indoor dry power distribution room

6. Advantages for Foreign Trade Website Promotion

Standard KYN28A-12 modular structure, compatible with international medium-voltage power distribution system standards;

High-precision metering transformers meet global grid metering certification requirements;

Independent sealed metering wiring compartment with anti-tampering design, widely recognized by overseas power grid clients;

Complete arc isolation and pressure relief design, high safety performance for industrial heavy-load projects;

Support 50/60Hz dual frequency customization, suitable for Asia, Africa, Southeast Asia and Middle East overseas projects;

Withdrawable PT trolley design, convenient maintenance and replacement without cutting off the whole busbar power supply;

Intelligent communication interface supports remote meter reading, matching modern intelligent power station construction demands.