The FDE outdoor oil immersed discharge coil is a single-phase tank-type unit for AC power systems at 50Hz/60Hz. It is connected in parallel with the high-voltage shunt capacitor bank. When the capacitor group is disconnected from the system, the coil provides a defined discharge path that reduces the residual voltage of the capacitor bank to a safe value within five seconds, protecting operating personnel and downstream equipment.
The live part is assembled in a sealed steel tank and immersed in transformer oil, with porcelain bushings bringing out the primary terminals. Oil insulation gives the unit excellent heat dissipation, lightning-impulse withstand capability and long service experience in outdoor capacitor bank installations. During normal operation the secondary winding functions as a voltage indicator; 3P and 6P secondary configurations are available so the winding can also feed residual-voltage relay protection for the bank.
Key Ratings Snapshot
| Item | Value |
|---|---|
| System frequency | 50Hz / 60Hz |
| Rated voltage ratio | 11/√3 : 0.1/√3 : 0.1/√3 kV |
| Accuracy class & rated output | 0.5/3P → 50/100VA; 0.5/6P → 50/100VA |
| Discharge capacity | 4 Mvar |
| Rated insulation level | 12/42/75 kV |
| Residual discharge time | < 5s to safe voltage |
| Ambient temperature | -40℃ ~ +40℃ |
| Altitude | ≤ 3000m |
| Phase / installation | Single phase / outdoor |
| Insulation medium | Mineral oil, sealed steel tank |
| Standard | DLT653-2009 and special customer demands |
Operating Function
The discharge coil is connected in parallel across the terminals of the high-voltage shunt capacitor bank, between the busbar and the neutral point of the bank. While the bank is energized the coil operates as a voltage transformer and its secondary winding supplies a proportional low voltage used for voltage indication or protection relays. When the capacitor bank is switched off, the stored electrostatic energy of the capacitors discharges through the coil windings; the residual voltage is drained to a safe level within five seconds.
Construction and Design
The FDE uses a classic oil-immersed construction: the core and windings are assembled in a gasketed steel tank filled with mineral oil, and the primary leads are brought out through outdoor porcelain bushings. Oil serves both as the insulation medium and the cooling medium, giving the unit strong over-voltage capability and a stable thermal rating. A separate secondary terminal box on the tank wall allows safe connection of the metering and protection circuits. The design conforms to DLT653-2009 and can be built to special customer demands.
Technical Parameters
Service Conditions
- Installation position: Outdoor type
- Ambient temperature: -40℃ ~ +40℃
- Altitude: Not more than 3000m
- System frequency: 50Hz / 60Hz
- Insulation medium: Mineral oil in sealed steel tank
- Atmosphere: No corrosive gas; no conducting or explosive dust
Technical Data
| Type | Rated
voltage ratio (kV) |
Accuracy class
& rated output (VA) |
Rated
insulation level (kV) |
Discharge
capacity (Mvar) |
|---|---|---|---|---|
| FDE-11/√3-1.7-1W | 11/√3:0.1/√3:0.1/√3 | 0.5/3P-50/100; 0.5/6P-50/100 | 12/42/75 | 4 / <5s |
Standards
- The products accord with the standards of DLT653-2009 and some special demands
- Rated frequency: 50Hz / 60Hz
- Rated insulation level: 12/42/75 kV
Installation & Wiring
Installation Diagram
The unit stands on a flat foundation with the tank base level; allow clearance around the tank for bushing creepage distances and for access to the secondary terminal box. Primary bushings connect to the capacitor bank neutral point and the busbar; the tank is connected to the earthing grid through the earth bolt. Refer to the approved outline drawing for foundation and busbar work.
Key Outline Dimensions
- Overall height: 605±10 mm (bushings included, 15° V-arrangement)
- Width over bushing terminals: 355±5 mm
- Base plate: 319 mm front-to-back × 262 mm side-to-side
- Mounting holes: 273±2 × 216±2 mm, Ø9 mm
- Primary terminals: 2-M10; secondary terminals: 4-M10 (1a, 1n, 2a, 2n)
- Earthing bolt: M8; pressure relief valve on tank wall
- Weight: approx. 47 kg
Wiring Diagram
The primary winding is connected between the bank neutral and earth (or across the designated winding section) as shown in the wiring diagram. The 3P/6P secondary windings supply voltage indication and residual-voltage protection circuits. Confirm terminal markings, polarity and earthing against the approved wiring drawing before energization.
Applications
- Outdoor HV shunt capacitor banks in substations and distribution networks
- Reactive power compensation and power-factor correction installations
- Capacitor bank protection schemes requiring 3P/6P secondary windings
- Pole-mounted and gable-frame capacitor banks at 50Hz/60Hz systems
Selection & FAQs
Selection Guide
- State the rated primary voltage. The standard type is 11/√3 kV; other ratios are available by agreement.
- State the capacitor bank capacity (Mvar). Match the coil to the bank; the standard unit covers a 4 Mvar discharge duty.
- Confirm system frequency. 50Hz or 60Hz.
- Choose the secondary configuration. 3P or 6P, accuracy class 0.5 with 50/100VA output, for indication and/or relay protection.
- Confirm the outdoor environment. Ambient -40℃~+40℃, altitude ≤3000m, insulation level 12/42/75 kV.
FAQs
Q1: What is the FDE discharge coil used for?
The FDE is connected in parallel with a high-voltage shunt capacitor bank. After the bank is disconnected from the system it reduces the residual voltage on the capacitors to a safe level within five seconds, and its secondary winding provides voltage indication or relay protection during normal operation.
Q2: What is the difference between oil immersed and dry type discharge coils?
An oil immersed coil uses mineral oil in a sealed steel tank as insulation and cooling medium, a time-tested outdoor construction with strong over-voltage capability. A dry type coil (e.g. FDGE11) is vacuum-cast with epoxy resin, is completely oil-free and needs no oil level checks. Both types discharge the capacitor bank to a safe voltage within five seconds.
Q3: What is the difference between the FDE and the FDGE11?
Both are single-phase outdoor discharge coils rated -40℃~+40℃ and altitude up to 3000 m. The FDE is the oil-immersed tank type with porcelain bushings and 3P/6P secondary options; the FDGE11 is the dry type fully-enclosed epoxy resin vacuum-cast unit, which is maintenance-free and oil-free.
Q4: How do I read the model designation FDE-11/√3-1.7-1W?
FD = discharge coil, E = with secondary winding, 11/√3 = rated primary voltage in kV, 1.7 = maximum matched capacitor capacity in Mvar, 1 = single phase, W = outdoor device.
Q5: How fast does the FDE discharge the capacitor bank?
The residual voltage is reduced to a safe level in less than five seconds at a discharge duty of 4 Mvar, in accordance with DLT653-2009.
Q6: Can special parameters be customized?
Yes. If the user’s data go beyond the ranges listed in the technical data table, they may be subject to an agreement between manufacturer and purchaser; voltage ratio, secondary configuration (3P/6P) and rated output can be agreed at order.