The FDGE8 semi-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 reduces the residual voltage of the capacitor bank to a safe value within five seconds. 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 coil adopts an iron-core semi-casting structure in which the core is built from high-grade silicon-steel sheets. The result is a compact, light-weight unit with low no-load loss, strong resistance to over-voltage, and convenient installation that requires no maintenance. It is designed as a maintenance-free replacement for conventional oil-immersed discharge coils in capacitor bank compensation installations.
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, protecting personnel and downstream equipment. 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 FDGE8 uses an iron-core semi-casting (semi-enclosed) structure. The magnetic core is stacked from high-grade silicon-steel sheets to keep no-load loss low and to provide strong over-voltage withstand capability. Windings are encapsulated by epoxy resin vacuum casting, giving a moisture-proof, maintenance-free insulation system suited to indoor switchgear and capacitor compartments. The semi-enclosed frame keeps the unit compact and light while allowing convenient mounting; base fixing holes and terminal arrangement suit standard capacitor bank layouts.
Model Designation
- FD — Discharge coil
- G — Dry type
- E — With secondary winding
- 8 — Design sequence number
- / □ — Rated primary voltage, kV
- □ — Maximum matched capacitor capacity, Mvar
- – 1 — Single phase
Example: FDGE8/11/√3-2.5-1 denotes a dry-type discharge coil with secondary winding, design No.8, 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 | ||||
| FDGE8/6.6/√3-1.7-1 | 6.6/√3/0.1 | 20 | 50 | 100 | 1.7 | 7.2/32/60 |
| FDGE8/7.2/√3-1.7-1 | 7.2/√3/0.1 | 1.7 | 7.2/32/60 | |||
| FDGE8/11/√3-1.7-1 | 11/√3/0.1 | 1.7 | 12/42/75 | |||
| FDGE8/11/√3-2.5-1 | 11/√3/0.1 | 2.5 | 12/42/75 | |||
| FDGE8/11/√3-3.4-1 | 11/√3/0.1 | 3.4 | 12/42/75 | |||
| FDGE8/12/√3-1.7-1 | 12/√3/0.1 | 1.7 | 12/42/75 | |||
| FDGE8/12/√3-2.5-1 | 12/√3/0.1 | 2.5 | 12/42/75 | |||
| FDGE8/12/√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): top width 180; height 530±5; base mounting 90 / 200±1 (front), 170 / 230±1 (side). 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 does the discharge coil do when the capacitor bank is switched off?
It provides a controlled discharge path so the capacitor bank residual voltage falls to a safe level within five seconds, protecting personnel and equipment.
Q2: 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.
Q3: 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.
Q4: 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.
Q5: Does it need maintenance?
No. The epoxy resin vacuum-cast, iron-core semi-casting design is maintenance-free, unlike oil-immersed discharge coils that require oil handling and testing.
Q6: What standard does the FDGE8 comply with?
It is manufactured in accordance with DL/T 653-1998, with load power factor cosφ 0.8 (lagging) and surface creepage distance greater than 300mm.