The FDGE9 fully-enclosed dry type discharge coil is an epoxy resin vacuum-cast, single-phase indoor product for AC power systems at 50Hz with a rated voltage of 10kV and below. 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 coil adopts a fully-enclosed cast structure in which the iron core, primary winding and secondary winding are cast together by advanced vacuum casting. During normal operation the secondary winding functions as a voltage indicator; where users require it, a residual voltage winding can be provided to deliver relay protection. The sealed body keeps the core and windings free of dust and moisture, giving a compact, light-weight, maintenance-free unit designed to replace conventional oil-immersed discharge coils.
Key Ratings Snapshot
| Item | Value |
|---|---|
| System frequency | 50Hz |
| Rated primary voltage | 6.6/√3, 7.2/√3, 11/√3, 12/√3 kV |
| Rated secondary voltage | 0.1 kV |
| Accuracy class / rated output | 0.2 → 20VA; 0.5 → 50VA; 1 → 100VA |
| Discharge capacity | 1.7 / 2.5 / 3.4 Mvar |
| Rated insulation level | 7.2/32/60 kV; 12/42/75 kV |
| Residual discharge time | ≤ 5s to safe voltage |
| Surface creepage distance | > 300mm |
| Load power factor | cosφ 0.8 (lagging) |
| Phase / installation | Single phase / indoor |
| Standard | DL/T 653-1998 |
Operating Function
The discharge coil is connected in parallel across the terminals of the high-voltage shunt capacitor 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. When the capacitor bank is switched off, the stored electrostatic energy of the capacitors discharges through the coil windings; the coil presents a controlled impedance path that drains the residual voltage to a safe level within five seconds. If a residual voltage winding is fitted, its output can drive a relay to provide unbalance or residual-voltage protection for the capacitor bank.
Construction and Design
The FDGE9 uses a fully-enclosed structure. The magnetic core is wound from high-grade cold-rolled silicon-steel sheet, and the core together with the primary and secondary windings is cast as one body by advanced vacuum casting technique. The result is a small-volume, light-weight unit with low no-load loss, strong resistance to over-voltage, and convenient installation that needs no maintenance. The fully-enclosed cast body seals the insulation system against dust and moisture, making the FDGE9 a maintenance-free replacement for oil-immersed discharge coils in capacitor bank compensation installations.
Model Designation
- FD — Discharge coil
- G — Dry type
- E — With secondary winding
- 9 — Design sequence number
- / □ — Rated primary voltage, kV
- □ — Maximum matched capacitor capacity, Mvar
- – 1 — Single phase
Example: FDGE9/11/√3-2.5-1 denotes a dry-type fully-enclosed discharge coil with secondary winding, design No.9, rated primary voltage 11/√3 kV, matched capacitor capacity 2.5Mvar, single phase.
Technical Parameters
Service Conditions
- Installation position: Indoor type
- Ambient temperature: -5℃ ~ +40℃
- Altitude: Not more than 1000m
- Atmosphere: No corrosive gas or smoke; no conducting or explosive dust
- Vibration: No severe mechanical vibration at the installation site
- Relative humidity: Monthly average ≤ 90%; daily average ≤ 95%
Technical Data
| Type | Rated
voltage (kV) |
Accuracy class
& rated secondary output (VA) |
Discharge
capacity (Mvar) |
Rated
insulation level (kV) |
||
|---|---|---|---|---|---|---|
| 0.2 | 0.5 | 1 | ||||
| FDGE9/6.6/√3-1.7-1 | 6.6/√3/0.1 | 20 | 50 | 100 | 1.7 | 7.2/32/60 |
| FDGE9/7.2/√3-1.7-1 | 7.2/√3/0.1 | 1.7 | 7.2/32/60 | |||
| FDGE9/11/√3-1.7-1 | 11/√3/0.1 | 1.7 | 12/42/75 | |||
| FDGE9/11/√3-2.5-1 | 11/√3/0.1 | 2.5 | 12/42/75 | |||
| FDGE9/11/√3-3.4-1 | 11/√3/0.1 | 3.4 | 12/42/75 | |||
| FDGE9/12/√3-1.7-1 | 12/√3/0.1 | 1.7 | 12/42/75 | |||
| FDGE9/12/√3-2.5-1 | 12/√3/0.1 | 2.5 | 12/42/75 | |||
| FDGE9/12/√3-3.4-1 | 12/√3/0.1 | 3.4 | 12/42/75 | |||
Standards
- DL/T 653-1998 《Specification of discharge coils for high voltage parallel connection capacitor for order》
- Load power factor: cosφ 0.8 (lagging)
- Surface creepage distance: more than 300mm
Installation & Wiring
Installation Diagram
Overall dimensions (mm): length 368; width 222±1; height 250; body diameter Ø185; base fixing 4-Ø12 with 25mm slot offset; top terminals 2-M10; side mounting M8. Refer to the approved outline drawing before foundation and busbar work.
Wiring Diagram
The primary winding is connected in parallel across the high-voltage capacitor bank terminals (phase to neutral/earth point of the bank). The secondary winding supplies voltage indication; where fitted, the residual voltage winding connects to the protection relay. Confirm terminal markings, polarity and earthing against the approved wiring drawing before energization.
Applications
- HV shunt capacitor banks in substations and distribution networks (6.6-12kV)
- Reactive power compensation and power-factor correction installations
- Capacitor bank protection schemes requiring residual-voltage relay input
- Indoor switchgear and capacitor compartments replacing oil-immersed discharge coils
Selection & FAQs
Selection Guide
- State the rated primary voltage. Choose from 6.6/√3, 7.2/√3, 11/√3 or 12/√3 kV to match the capacitor bank system voltage.
- State the capacitor bank capacity (Mvar). Select the matched discharge capacity 1.7, 2.5 or 3.4 Mvar; do not order by model code alone.
- Confirm system frequency and secondary use. 50Hz; specify whether the secondary is for voltage indication only or whether a residual voltage winding is required for relay protection.
- Specify accuracy class and burden. 0.2 (20VA), 0.5 (50VA) or 1 (100VA) according to the connected metering/protection load.
- Confirm insulation level and environment. 7.2/32/60 or 12/42/75 kV; verify indoor installation, altitude ≤1000m and ambient -5℃~+40℃.
FAQs
Q1: What is the difference between the FDGE9 and the FDGE8?
Both are indoor epoxy resin vacuum-cast dry type discharge coils, but the FDGE9 is a fully-enclosed structure in which the core and windings are cast as one sealed body, while the FDGE8 is a semi-enclosed iron-core semi-casting design. The FDGE9 offers higher protection against dust and moisture.
Q2: How fast does the FDGE9 discharge the capacitor bank?
When the capacitor bank is switched off, the coil reduces the residual voltage to a safe level within five seconds, in line with DL/T 653-1998.
Q3: Can the secondary winding be used for voltage indication?
Yes. During normal operation the secondary winding outputs a proportional low voltage suitable for voltage indication, with accuracy class 0.2, 0.5 or 1.
Q4: Is relay protection available?
On request a residual voltage winding can be provided to supply a relay for residual-voltage / unbalance protection of the capacitor bank.
Q5: Which voltage ratings and capacities are available?
Rated primary 6.6/√3, 7.2/√3, 11/√3 and 12/√3 kV with matched discharge capacities of 1.7, 2.5 and 3.4 Mvar; insulation level 7.2/32/60 or 12/42/75 kV.
Q6: Does the FDGE9 need maintenance?
No. The fully-enclosed epoxy resin vacuum-cast design is maintenance-free and oil-free, unlike oil-immersed discharge coils that require oil handling and testing. It is manufactured in accordance with DL/T 653-1998.