The PT cabinet is a familiar piece of equipment for those in the electrical industry. We often encounter PT cabinets in electrical engineering projects. So, what exactly is a PT cabinet, and what role does it play in the system? Let's delve into the PT cabinet.

▌01 Definition and Functions of PT Cabinet

1. Definition of PT Cabinet

The PT cabinet, also known as the busbar voltage transformer cabinet or voltage transformer cabinet, typically houses a set of voltage transformers, a circuit breaker, surge arresters, and other primary electrical components. The circuit breaker's fuse provides protection for the voltage transformer. A voltage transformer converts high voltage to low voltage at a specified ratio to meet the voltage requirements of instruments.

Surge arresters primarily protect against overvoltage and lightning strikes.

PT cabinets usually adopt a modular design. Depending on the project's specific design parameters, different types and quantities of PTs can be configured.

The overall structure of the PT cabinet features a detachable metal-clad design, with large observation windows on the equipment panel for monitoring the cabinet's operation. Each PT unit has a compartment, with primary and secondary circuits adopting a tap-changer design to separate the primary and secondary compartments. The cabinet is aesthetically pleasing and reliable, facilitating on-site maintenance.

In simpler terms, the PT cabinet provides the voltage for the busbar in the high-voltage cabinet overhead. The PT cabinet contains both measuring and metering PTs (previously required to be separate due to standards specifying higher grades for metering transformers than protection transformers, but now can be combined unless specified otherwise). These PTs supply voltage for measurement, metering, and protection to other high-voltage cabinets.

The overhead busbar also includes a 220V DC busbar (voltage sourced from the DC panel, providing DC power for circuit breakers, integrated protection, and other equipment) and a 220V AC busbar (voltage also sourced from the AC output of the DC panel, providing AC power for cabinet lighting, heaters, and other devices).

2. Functions of PT Cabinet

Provides measurement, instrument voltage, and protection voltage in electrical systems.

Supplies measuring voltage for power meters.

Offers operational and control power (PT) for related equipment.

Meets the requirements for electrical system relay protection, including busbar insulation, undervoltage, overvoltage, standby device self-switching conditions, etc. The overhead busbar in the high-voltage cabinet is powered by the PT cabinet.

▌02 Differences and Configuration Schemes between PT Cabinet and Metering Cabinet

1. Differences between PT Cabinet and Metering Cabinet

A PT cabinet, which stands for Potential Transformer cabinet, is typically used to house voltage transformers connected to the busbar for measurement and protection purposes.

To accurately meter and effectively manage consumption for each user, power companies install a dedicated metering cabinet on the user's side. This cabinet contains voltage transformers, current transformers, and metering instruments. The data from these meters is used for billing, and only power companies have the authority to maintain and debug the metering cabinet.

2. Common Configuration Schemes for PT Cabinet

No 1 & 2: Common configurations for the KYN28 cabinet (handcart cabinet).

No. 1 uses a circuit breaker handcart, with surge arresters and circuit breakers installed inside the handcart. PTs are fixed below the cable compartment or mounted on the rear beam of the cable compartment, with the neutral point of the PT grounded through a damping resistor.

No. 2 uses a PT handcart, with PTs, circuit breakers, surge arresters, and damping resistors all installed inside the handcart. The neutral point of the PT is grounded through a damping resistor.

No. 3: Common configurations for the HXGN-12 cabinet (fixed cabinet).

No. 3 uses an isolation switch as the main switch for PT. For 10kV equipment, GN30 or GN19 products are used, and for 35kV equipment, GN27 products are chosen. PTs are fixed at the bottom of the switch cabinet, with the neutral point grounded through a damping resistor.

Due to the low current passing through the main circuit of the PT cabinet (with a rated current of the protection circuit breaker