PT Handcart

TOONICE’s the PT Handcart, whose full name is High-Voltage Potential Transformer handcart, is one of the core devices in the power system for voltage measurement, protection, and control. It is mainly installed in high-voltage switchgear cabinets and is characterized by mobility and easy maintenance.

I.Structure and Principle

1. Components:

① Primary Part: Includes potential transformer (PT), high-voltage fuse (such as XRNP1 fuse element), contact arm, and contact head. The contact arm is connected to the busbar, and the fuse is used for short-circuit protection.

② Secondary Part: Outputs a voltage of 100V through the low-voltage winding, divided into two groups of wye connection (for measurement and metering) and one group of open delta connection (for zero-sequence voltage detection).

③ Mechanical Structure: Chassis trolley, casing, insulator, propulsion mechanism (such as lead screw and nut), which supports the trolley to move and lock in position within the switchgear cabinet.

2. Working Process:

① Voltage Transformation: The power from the high-voltage busbar passes through the contact arm → fuse → primary winding of PT, stepping down the high voltage to 100V and then outputting it to the secondary circuit.

② Fault Response: During normal operation, the voltage of the open delta is 0; when single-phase grounding occurs, the zero-sequence voltage triggers the protection device to operate via the open delta.

II.Design Advantages and Technical Features

1. Modular Design:

① The trolley can be entirely pulled out of the cabinet, and PT or fuses can be replaced without power outage, greatly reducing maintenance time.

② It is compatible with the size of circuit breaker trolleys, facilitating standardized configuration of switchgear cabinets.

2. Safety Protection:

① The casing adopts a metal-enclosed structure and has an IP protection rating to prevent foreign objects from intruding and electric shock risks.

② The secondary circuit is equipped with independent disconnecting points to prevent reverse power transmission from the secondary side endangering primary equipment.

3. Technical Parameters:

① Voltage Rating: Common ratings are 12kV and 40.5kV, suitable for different power grid requirements.

② Insulation Level: Power frequency withstand voltage is 42kV (1 minute), lightning impulse withstand voltage is 75kV (peak value), meeting the requirements of high-voltage environments.

③ Accuracy Class: Class 0.2 (for metering), Class 0.5 (for measurement), 3P/6P (for protection), selected according to application scenarios.

III. Functions and Positioning

1. Core Roles

① Convert high voltages in the power grid (such as 10kV, 35kV) proportionally into low voltages (such as 100V) for use in secondary circuits (such as protection devices, metering devices, and control equipment).

② Fault Detection: Detect the zero-sequence voltage in the system through the open delta connection. When a single-phase grounding fault occurs, the zero-sequence voltage is generated to trigger protection tripping and ensure power grid safety.

2. Application Scenarios

① Substations and Power Plants: Monitor bus voltage and provide signals for relay protection and automatic devices.

② Photovoltaic (PV) and Wind Power Step-up Stations: Meter generated electricity and monitor the voltage stability of the system.

③ Industrial Power Distribution Systems: Ensure that the equipment operating voltage is within a safe range.