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What is the difference between a PT cabinet and a metering cabinet?

Release time:

2025-05-17

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Abstract

PT cabinets (voltage transformer cabinets) and metering cabinets are two key devices in power distribution systems. Although both involve voltage transformers (PTs), their functions, components, and application scenarios differ significantly. The following is a detailed comparison of the two:

1. Core Functional Differences between PT Cabinets and Metering Cabinets

Function	PT Cabinet	Metering Cabinet
Main Function	Provides voltage measurement, voltage protection, and operating power, supporting relay protection and system monitoring.	Specifically used for electricity metering, accurately calculating electricity consumption and serving as the basis for electricity billing.
Voltage Signal Processing	Converts high voltage to low voltage (e.g., 10kV→100V) for use by instruments, protection devices, and control circuits.	In conjunction with current transformers (CTs) and voltage transformers (PTs), calculates electrical energy (power × time).
Protection Function	Provides overvoltage, undervoltage, busbar insulation monitoring, and other protections; supports automatic switching of backup equipment.	No direct protection function, but it is necessary to ensure the accuracy of metering data and prevent electricity theft or metering errors.
Power Supply Target	Provides power to the measurement, protection, and control circuits of other high-voltage cabinets (e.g., top busbars).	Serves only metering devices (e.g., electricity meters), does not provide other power sources.

2. Composition and Configuration of PT Cabinets and Metering Cabinets

Components	PT Cabinet	Metering Cabinet
Voltage Transformer (PT)	Essential, used to convert high voltage to low voltage (e.g., 100V).	Essential, but with higher accuracy requirements (usually 0.2S class) to ensure metering accuracy.
Current Transformer (CT)	None.	Essential, used to measure current and calculate electrical energy.
Protection Devices	Includes fuses or circuit breakers (protecting the PT secondary circuit) and surge arresters (protection against lightning strikes and overvoltage).	Usually no independent protection devices, but sealing and anti-theft devices are required (to prevent human interference).
Other Components	Isolating switches, detuning devices (suppressing ferromagnetic resonance), and energized indicators (some schemes).	Energized indicator (monitoring whether it is energized), metering instruments (such as electricity meters), and sealing devices.
Structural Design	Removable metal armored structure, the panel has an observation window, and supports trolley-type maintenance (e.g., KYN28 scheme).	Mostly fixed structure, the panel is tightly sealed, and users cannot open it without authorization (managed by the power department).

3. Management Permissions and Application Scenarios of PT Cabinets and Metering Cabinets

Features	PT Cabinet	Metering Cabinet
Management Permissions	Managed by users or maintenance personnel; allows for daily maintenance and debugging.	Exclusively managed by the power department; users have no right to repair or adjust; requires sealing protection.
Installation Location	Usually located behind the incoming line cabinet and in front of the feeder cabinet; only the main busbar passes through; no direct outgoing lines.	Installed on the user side (e.g., high-voltage outgoing line cabinet or connecting cabinet), directly connecting the user load and the power grid.
Data Usage	Data is used for system monitoring, relay protection, and operational control.	Data is directly used for electricity billing; requires high accuracy and legal validity.
Configuration Flexibility	Measurement PTs and metering PTs can be configured as needed (can be shared or separate); supports multiple wiring methods (e.g., V/V).	Fixed configuration; must meet metering standards (e.g., GB/T 16934-2013); usually uses a high-supply, high-metering scheme.

4. Typical Configuration Schemes

Common PT Cabinet Schemes

Scheme 1 (Fuse Trolley)
- Surge arresters and fuses are installed inside the trolley; the PT is fixed below the cable compartment or on the rear beam.
- The PT neutral point is grounded via a primary detuning device.
Scheme 2 (PT Trolley)
- The PT, fuses, surge arresters, and detuning devices are all integrated into the trolley; the neutral point is grounded through a grounding electrode.
Scheme 3 (Fixed Cabinet)
- The isolating switch serves as the main switch (e.g., GN30/GN19); the PT is fixedly installed at the bottom of the cabinet; the neutral point is grounded.

Typical Metering Cabinet Configuration

High-supply, high-metering: Voltage transformers (PTs) and current transformers (CTs) are both installed on the high-voltage side, directly connected to the electricity meter.
High-supply, low-metering: The PT is installed on the high-voltage side, and the CT is installed on the low-voltage side; electrical energy is calculated through conversion.

5. Key Technical Parameters

Parameters	PT Cabinet	Metering Cabinet
Accuracy Class	Protection class (1.0 class) or measurement class (0.5 class).	Metering class (0.2S class), error < ±0.2%.
Insulation Withstanding Voltage	≥32kV (50/60Hz, 1 minute).	Same requirements as PT cabinet, but additional consideration for the insulation performance of the energy meter is needed.
Short Circuit Protection	Secondary side fuse or circuit breaker (e.g., RN1 type fuse).	No independent short circuit protection; relies on CT and PT configuration.
Lightning Protection	Surge arrester (e.g., YH5WZ-17/45) installed on the high-voltage side.	Usually no surge arrester, but the lightning protection capability of PT and CT needs to be ensured.

6. PT Cabinet and Metering Cabinet Practical Application Examples

PT Cabinet Application Scenarios:

Substation bus voltage monitoring.
Relay protection power supply for high-voltage switchgear (e.g., overvoltage protection, automatic switching of backup power supply).
Voltage fluctuation analysis of factory power distribution systems.

Metering Cabinet Application Scenarios:

High-voltage user-side electricity metering for commercial buildings and factories.
Electricity consumption statistics and electricity billing for users by power companies.
Industrial equipment requiring precise metering (e.g., data centers, production lines).

7. Summary Comparison of PT Cabinet and Metering Cabinet

Comparison Item	PT Cabinet	Metering Cabinet
Core Function	Voltage measurement, relay protection, operating power supply.	Electricity metering, electricity billing.
Key Components	PT, fuse, surge arrester, isolating switch.	PT, CT, energy meter, sealing device.
Management Permissions	Maintainable by user/maintenance personnel.	Exclusive management by the power department; users have no access.
Installation Location	Main bus side; no direct outgoing lines.	User-side outgoing lines or connecting cabinets; directly connected to the load.
Data Usage	System monitoring and protection.	Legally valid basis for electricity billing.

Each has its own specialization in the power system. PT cabinets focus on voltage transformation and system protection, while metering cabinets focus on precise electricity metering. The two are usually used together, with the PT cabinet providing voltage signals to the metering cabinet, ensuring the safe and economical operation of the power system.

Key words:

How to choose a home distribution box?

PT cabinet function and composition

Hunan Chengyuan Electrical CO.,LTD