The FDE high altitude outdoor oil immersed discharge coil is a single-phase tank-type unit for AC power systems at 50Hz/60Hz, engineered for capacitor bank installations at altitudes up to 5000 m above sea level. 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 bank to a safe value within five seconds, protecting operating personnel and downstream equipment.
At high altitude the air is thinner, so external insulation withstand and heat dissipation both become harder than at sea level. This version therefore uses outdoor porcelain bushings with enlarged creepage distance and increased air clearances, together with an oil-filled sealed steel tank that carries the internal insulation and the thermal load. The primary terminals are brought out through two bushings inclined at 19° each in a V arrangement, and the secondary winding serves as a voltage indicator during normal operation, with 3P and 6P configurations available for residual-voltage relay protection.
Key Ratings Snapshot
| Item | Value |
|---|---|
| Type designation | FDE-11/√3-4.0-1W |
| System frequency | 50Hz / 60Hz |
| Rated voltage ratio | 11/√3 : 0.1/√3 : 0.1/√3 kV |
| Matched capacitor capacity | 4.0 Mvar |
| 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 | ≤ 5000m (high altitude version) |
| Phase / installation | Single phase / outdoor |
| Insulation medium | Mineral oil, sealed steel tank |
| Total weight | Approx. 84 kg |
| 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 core and windings are assembled inside a gasketed sealed steel tank filled with mineral oil, which acts as both the insulation medium and the cooling medium and gives the unit strong lightning-impulse withstand capability. For high altitude service the external insulation is reinforced: the outdoor porcelain bushings have longer creepage paths and the top terminals use a 2-M12 connection with increased air clearance, with the two bushings set at 19° + 19° in a V arrangement. The tank is provided with an oil filling port and a pressure relief valve, an earthing bolt on the tank wall, a separate secondary terminal box, and lifting lugs for handling. Overall weight is approximately 84 kg. 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 5000m (high altitude version)
- 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/√3-4.0-1W | 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 the reinforced bushing creepage distances and for access to the secondary terminal box and the pressure relief valve. Primary bushings connect to the capacitor bank neutral point and the busbar; the tank is connected to the earthing grid through the earthing bolt. At high altitude sites, keep the specified air clearances to grounded structures, since thinner air lowers the external insulation withstand of bare gaps. Refer to the approved outline drawing for foundation and busbar work.
Wiring Diagram
The primary winding is connected between the bank neutral and earth as shown in the wiring diagram. The 3P/6P secondary windings supply voltage indication and residual-voltage protection circuits, with the open-delta (da/dn) terminals feeding the protection relay. Confirm terminal markings, polarity and earthing against the approved wiring drawing before energization.
Key Outline Dimensions
- Overall height: 750 mm (primary bushings included)
- Primary bushings: inclined 19° + 19° in V arrangement, top terminal 2-M12
- Bushing center span: 360 mm; tank width 340 mm (front view); side base 360 mm, bushing offset 100 mm
- Cover outline: 400 mm × 360 mm, 325 mm between bushing flange centres
- Mounting holes: 215 mm spacing, 13 mm wide slots, 4 off (M10)
- Earthing: M8 earthing bolt on tank wall
- On cover: oil filling port and pressure relief valve; on tank wall: nameplate
- Weight: approx. 84 kg
Applications
- Outdoor HV shunt capacitor banks on substations at high altitude (plateau, mountain and hilly regions)
- Reactive power compensation and power-factor correction installations up to 5000 m above sea level
- Capacitor bank protection schemes requiring 3P/6P secondary windings
- Newly built or retrofitted 10 kV class capacitor banks where the standard 3000 m rating is not sufficient
Selection & FAQs
Selection Guide
- State the site altitude. This version is rated for up to 5000 m; for sites at or below 3000 m the standard FDE-11/√3-1.7-1W is usually the more economical choice.
- State the rated primary voltage. The standard type is 11/√3 kV; other ratios are available by agreement.
- State the capacitor bank capacity (Mvar). The 4.0 in the type designation is the matched bank capacity; the discharge duty is 4 Mvar.
- Choose the secondary configuration. 3P or 6P, accuracy class 0.5 with 50/100VA output, for indication and/or relay protection.
- Confirm system frequency and environment. 50Hz or 60Hz, ambient -40℃~+40℃, insulation level 12/42/75 kV.
FAQs
Q1: How do I read the model designation FDE-11/√3-4.0-1W?
FD = discharge coil, E = with secondary winding, 11/√3 = rated primary voltage in kV, 4.0 = maximum matched capacitor capacity in Mvar, 1 = single phase, W = outdoor device.
Q2: What is the difference between this high altitude version and the standard FDE?
Both are single-phase outdoor oil-immersed units with the same 11/√3 kV ratio and 12/42/75 kV insulation level. The high altitude version is rated for sites up to 5000 m instead of 3000 m, uses reinforced external insulation with longer bushing creepage and larger air clearances, matches a 4.0 Mvar bank instead of 1.7 Mvar, and is physically larger at about 84 kg against about 47 kg. See the standard FDE Outdoor Oil Immersed Discharge Coil page for the 3000 m version.
Q3: Why does the technical table show 4 Mvar while the type says 4.0?
The 4.0 in the type designation is the matched capacitor bank capacity in Mvar, and the discharge capacity in the table is the corresponding 4 Mvar discharge duty within five seconds, so the two figures agree for this model. On the 1.7 type the matched bank is smaller while the discharge duty remains 4 Mvar.
Q4: Which secondary configuration should I choose, 3P or 6P?
Choose 3P when the secondary winding is needed for voltage indication plus an open-delta residual-voltage protection supply. Choose 6P when the protection scheme also needs the third harmonic or a more complete residual voltage signal on the bank neutral side. Both are accuracy class 0.5 with 50/100VA rated output.
Q5: Can single-phase units be applied on a three-phase capacitor bank?
Yes, one coil per phase, three units in total. If you prefer a single three-phase common-tank unit instead, look at the FDGEC Outdoor Three-Phase Oil Immersed Discharge Coil, which is built for 35 kV class double-section banks.
Q6: What data do I need to provide when ordering?
Please state the system rated voltage and frequency, the capacitor bank capacity and connection method, the actual installation altitude, the number of secondary windings with accuracy class and rated output, and any special environmental conditions such as severe cold, salt mist or seismic requirements. Data beyond the ranges in the technical table are agreed between manufacturer and purchaser.