Three-phase Oil-immersed Outdoor Electric Power Metering Box 10kV-35kV

Overview of the Main Structure of 10kV Oil-immersed High-voltage Metering Box

• The product consists of a combined transformer and a metering instrument box. The combined transformer is assembled with two voltage transformers and two current transformers. The metering instrument box is equipped with D86 series three-phase electricity meters and fuses. For unidirectional metering, one active energy meter and one reactive energy meter are provided; for bidirectional metering, two active energy meters and two reactive energy meters are provided.
• The iron core of the voltage transformer is of external type, laminated with high-quality cold-rolled oriented silicon steel sheets. The middle limb is multi-stage stepped, with primary and secondary windings mounted on it.
• The iron core of the current transformer is of internal type, laminated with high-quality cold-rolled oriented silicon steel sheets, with primary and secondary windings mounted on the core limb.
• The primary terminals of the voltage and current transformers are led out for connection via conductive rods inside porcelain insulators. Both voltage and current transformers are fixed on a support plate, which is suspended on the tank cover by support rods and immersed in transformer oil.
• High-voltage lead bushings and secondary lead bushings are installed on the tank cover. An oil drain plug and an earthing bolt are mounted on the side of the oil tank.
• The instrument box is installed on the front of the oil tank, with an observation window and a sealing hole.
• The multi-ratio metering box adopts a secondary ratio-changing compound structure, enabling more convenient and efficient ratio adjustment.
• The multi-ratio metering principle adopts V/V-12 wiring. The secondary point b in the voltage circuit is earthed, and the tail ends of the secondary current circuits of phases A and C are earthed.Inside the multi-ratio metering box, the tail ends of the secondary current circuits and the tail end b of the secondary voltage circuit have been connected together but not earthed. During actual measurement, this point (b) shall be reliably earthed.

Acceptance and Pre-operation Inspection

• Visual Inspection: The product shall be well sealed, porcelain parts free from damage, and factory documents (Certificate of Quality, Operation Manual) complete.
• Measure the insulation resistance between primary winding and ground with a 2500V megger. The value shall be not less than 1000 MΩ (air humidity ≤ 75%).
• Short-time power frequency withstand voltage test: The test voltage shall be 80% of the factory test voltage.
• If the product has been stored for a long time, it must be inspected according to Clauses 5.1, 5.2 and 5.3 before use.
• Check and calculate whether the load matches before installation. Installation shall comply with the marked load rating.

Operation Method and Cautions

• When used for metering branch line energy or assessing line loss, the metering box may be mounted on a pole support.
• When used for metering energy on the high-voltage side of a power transformer, it may be installed on the same platform as the transformer or on a utility pole.
• If reverse phase sequence occurs during operation of a newly installed metering box, the active energy meter will still run forward while the reactive energy meter runs backward, resulting in metering error. Swap any two high-voltage side cables to restore correct phase sequence for accurate metering.
• When used for energy metering on a two-phase-one-ground power line, connect the ground wire to phase B of the metering box, and connect the other two phases in correct phase sequence to avoid additional metering errors.
• Use only the lifting lugs on the oil tank for hoisting.
• The secondary terminal point b of the combined transformer and the earthing bolt on the oil tank must be reliably earthed to prevent accidents.

Maintenance and Servicing

• Regular inspections shall be performed on metering boxes in operation. If oil shortage or oil deterioration is found, filter, replace or refill with new oil immediately.
• Before use, the metering box shall be properly stored in a warehouse with a temperature range of -25℃ to +40℃, relative humidity ≤ 85%, good ventilation and no corrosive gases.