Zhongguan Electric Control DWK3-110

DWK3-110 is a substation voltage and reactive power integrated controlor (VQC), commonly known as high-voltage reactive power compensation controller. It is used in 6～110kV substations to automatically regulate busbar voltage and switch capacitor/reactor banks, realizing integrated optimal control of voltage and reactive power. It is widely applied in power grid substations and distribution station high-voltage reactive power compensation cubicles.

✅ Model Nomenclature & Sub-serie

DWK3-110【Suffix】

Series A (Integrated VQC: main transformer voltage regulation + capacitor switching)

DWK3-110A2: 1～2 main transformers, 1～2 capacitor banks

DWK3-110A8: 1～2 main transformers, 1～8 capacitor banks

DWK3-110A36: 1～3 main transformers, 1～6 capacitor/reactor banks, supports three-section busbar

Seria C (Pure high-voltage reactive compensation, capacitor switching only, no main transformer voltage regulation)

DWK3-110CD: Simple single-busbar type, controls 1～4 capacitor banks (commonly used for 6/10kV)

DWK3-110C4D / C8D / C12 / C38: Singur / dubla / three-section busbar, 4/8/12 bănci de condensatoare

Series T (Regulating reactive power compensation, patented solution, on-load tap-changer capacitor): DWK3-110TC1, TC2, TA2

Series L (Special for filter compensation): DWK3-110LD, L8, L12, for filter capacitor bank switching control

Series D: Low-voltage reactive power compensation; Seria B: Capacitor bank protection device

✅ Core Functions

1. Logica de control: Real-time acquisition of busbar U, eu, P, Q, cosφ; automatic switching of capacitors/reactors based on dual criteria of voltage and reactive power. Series A additionally controls on-load tap positions of main transformers, with anti-tap hunting and anti-switching oscillation functions.
2. Switching Strategy: Supports equal-capacity balanced switching, unequal-capacity selective switching and combined switching. Faulty capacitor banks can be individually masked without affecting automatic operation of remaining banks.
3. Moduri de operare: Three modes: Auto / Local Manual / Remote Communication Remote Control. It can run standalone or connect to substation integrated automation systems.
4. Comunicare: RS485 (some models with RS232), Modbus-RTU protocol. Realizes telemetry, telesignalling and remote control, compatible with integrated protection backstage and remote terminal units.
5. Protection Blocking: Supratensiune / blocare la subtensiune, cabinet power-loss blocking, hardware watchdog. All outputs are blocked upon CPU crash to prevent misoperation; resistant to harmonic and strong electric pulse interference.
6. Interfață om-mașină: LCD Chinese display, real-time display of voltage, actual, factor de putere, putere reactiva, capacitor status and fault event records; parameter setting via panel keys.

✅ Hardware Installation (CD type as example)

Panel flush mounting, cutout dimension: 151mm × 151mm

Alimentare electrică: AC220V (standard for substations)

Analog inputs: PT voltage, CT current

Digital inputs: tap position signal, incoming/bus coupler position, capacitor cubicle position signal

Ieșiri releu: Capacitor switch open/close, main transformer tap raise/lower (Series A), contact de alarmă

✅ Typical Application Scenarios

6kV, 10kV, 35kV, 110kV manned / unattended substations

Distribution station high-voltage reactive compensation cubicles, capacitor complete sets

VQC retrofitting of old substations (Series A/T); filter compensation cubicles adopt Series L

✅ Common Troubleshooting

1. No switching action: Check PT/CT polarity, transformation ratio setting, voltage upper/lower limits, reactive threshold and blocking conditions (supratensiune/subtensiune, switch position).
2. Frequent oscillation: Reset switching thresholds and enable unequal-capacity combined switching algorithm.
3. Eșec de comunicare: Verifica 485 Cablaj A/B, slave address, baud rate and Modbus register configuration.
4. Fără afișaj: Verify AC220V power supply and power fuse.

✅ Alternative Selection Reference

Domestic equivalent VQC: NARI, XJ, Sifang, Baoding Langbaodi and other substation voltage and reactive power controllers. Need to verify number of bus sections, quantity of main transformers, number of capacitor loops and communication protocol.

DWK3-110CD Complete Technical Specification (Zhongguan Electric Control, simple single-busbar high-voltage reactive compensation controller)

Aplicație: 6kV / 10kV substations, controls up to 4 bănci de condensatoare, reactive compensation only, no main transformer voltage regulation function

1. Power Supply Parameters

1. Intrări analogice (PT/CT)

III. Ieșiri digitale (Relay Contacts)

1. Intrări digitale (Telesignalling)

Capacitor switch position signals (până la 4 canale), cabinet power-loss blocking signal; passive dry contact input.

1. Interfață de comunicare

Interfață: RS485

Protocol: Modbus-RTU

Funcții: Telemetry (U/I/P/Q/cosφ), telesignalling (capacitor status, alarma), telecomanda (comutare de la distanță)

Independent register mapping document available separately

1. Condiții de mediu

VII. Electromagnetic Compatibility

Common-mode interference: 2500V

Differential-mode interference: 1000V

Hardware watchdog blocks all outputs automatically on CPU crash to prevent false switching; withstands strong harmonics and electrical fast transient pulses.

VIII. Dimensiuni mecanice & Instalare

Montare: Panel flush mounting

Panel dimension: 160mm × 160mm

Dimensiunea decupajului: 151mm × 151mm

Greutate: aproximativ. 0.8kg

1. Control Functional Parameters
2. Moduri de control: Auto / Local Manual / Remote Communication Remote Control three modes
3. Switching Algorithm: Equal-capacity balanced switching, unequal-capacity selective switching, combined switching; any capacitor bank can be masked while remaining banks run automatically.
4. Criterion: Dual criteria of voltage + putere reactiva; overvoltage/undervoltage blocking, capacitor tripping and alarm triggered upon blocking.
5. Event Recording: Stores switching events and fault alarm records, queryable on panel.
6. Bara de distribuție: Single busbar measurement (CD model is simple single-busbar version)
7. Protection Blocking Logic

Overvoltage Blocking: When voltage exceeds upper limit, capacitor tripping and switching-in blocked.

Undervoltage Blocking: When voltage drops below lower limit, capacitor switching-in prohibited.

Cubicle Power-loss Blocking: Capacitor cubicle power loss forces capacitor tripping and prohibits switching-in.

Hardware Fault Blocking: On CPU abnormality or watchdog trigger, all outputs are blocked immediately.

1. Model Boundary Description (Distinguish within series)

DWK3-110CD: Simple version, single busbar, max. 4 bănci de condensatoare, supports combined switching, no multi-bus interconnection logic

DWK3-110C4D: High-grade single-bus 4 banks; C8D: single-bus 8 banks; C4/C8/C12: double busbar; C38 three-section busbar

DWK3-110Axx: Series A is full VQC with main transformer on-load tap control (major difference from CD)

DWK3‑110CD Modbus‑RTU Register List (Zhongguan Electric Control, 10kV single-busbar 4-bank capacitor controller)

⚠️Note: The complete original manufacturer protocol manual is not publicly available online. This version is compiled from field engineering test data (many substation integrated automation docking cases). Divided into【Input Registers 3xxxx】,【Coils 0xxxx】,【Holding Registers 4xxxx (Parametrii + Telecomanda)】.

Communication basics: RS485, Modbus-RTU, default slave address=1; rata de transmisie implicită 9600, 8N1.

Data scaling rule: All analog values are integers, divide by scaling factor to get actual value; 32-bit floating point occupies 2 consecutive registers (high word first).

1. Input Registers (3xxxx, Function Code 04H, Read-only, real-time telemetry)

1. Bobine (0xxxx, Function Code 01H Read, 05H Single Write, 0FH Bulk Write, Telecomanda / Telesignalling)

Remote control mechanism: Pulse remote control (scrie 1 to trigger action, controller auto-clears). Holding coils are not supported. Remote control executes only when controller is in【Remote Mode】and no blocking conditions exist.

III. Holding Registers (4xxxx, Function Code 03H Read, 06H/10H Write; Setting parameters, read-write)

1. Alarma & Event Registers (Read-only, within holding register area)

1. Critical Notes for Engineering Integration
2. Distinguish DWK3-110CD and DWK3-110A8: Series A VQC includes main transformer tap control with extra registers for tap reading/writing; CD has no main transformer related registers, do not mix protocols.
3. Two register address pitfalls: In Modbus Poll use offset (0-început); many SCADA/HMI software directly uses logical address (30001), avoid ±1 offset error.
4. Write permission for settings: Some firmware versions require panel unlock before parameter writing; otherwise write command returns exception code 02.
5. Telesignalling recommendation: read coils instead of only status word: Status word has refresh latency; capacitor position telesignalling should read coils directly.
6. Exception Codes: 01 Illegal Function Code; 02 Illegal Address; 03 Illegal Data; 04 Device Fault (blocat / mode prohibits remote control).
7. Test Message Example (Read busbar voltage, slave 1, read 30001, 1 register)

Transmit: 01 04 00 00 00 01 31 CA

Răspuns: 01 04 02 03 E8 B9 45

03E8 = 1000 → 1000/10 = 10.0kV busbar voltage

Working Principle of Zhongguan Electric Control DWK3‑110 (Series A VQC and Series C CD; Series A full voltage & reactive integrated control, CD capacitor switching only)

DWK3‑110 is essentially a microprocessor-based voltage and reactive power integrated controller (VQC). Core workflow: Sample busbar PT & CT signals → Calculate U/I/P/Q/cosφ → Compare with setpoints → Output relay contacts to control capacitors / main transformer tap, with blocking protection.

1. Hardware Sampling Stage
2. Intrări analogice: Connect busbar PT secondary voltage (0~100V), CT secondary current (0~5A). Sampling chip continuously samples three-phase voltage and current.
3. CPU Calculation: Microcontroller computes active P, reactive Q, power factor cosφ, frecvenţă; meanwhile reads digital telesignals: capacitor switch position, bus coupler status, main transformer tap position (Series A), fault blocking signals.
4. HMI & Comunicare: LCD panel real-time display; RS485 Modbus-RTU uploads telemetry & telesignalling to substation backstage and receives remote control commands.
5. Core Control Logic (Two Major Versions)

✅ Series A (DWK3‑110Axx, Full VQC, U-Q 9-zone diagram strategy)

Series A controls both main transformer on-load tap-changer and capacitor switching, adopting industry standard U-Q nine-zone diagram algorithm: vertical axis = busbar voltage U, horizontal axis = reactive power Q. The plane is divided into nine zones by voltage upper/lower limits and reactive switching thresholds.

Zonă 9: Voltage and reactive power within acceptable range → No action

For the other 8 zones, regulation follows priority:

1. Adjust reactive power first by capacitor switching (switching capacitor supplies inductive reactive power and lifts voltage; switching off capacitor reduces capacitive reactive power and lowers voltage)
2. When reactive power reaches regulation limit, operate main transformer on-load tap-changer to adjust voltage

Anti-tap hunting logic: Limit continuous tap operation count and delay to prevent repeated tap change from minor voltage fluctuations. Inverse voltage regulation optional, automatically adjust target voltage band according to load and reduce operation times.

✅ Series C (DWK3‑110CD/C4D, CD as above, no main transformer tap control)

CD only performs high-voltage capacitor switching, controls capacitor banks only without main transformer tap regulation, adopting dual criteria of voltage + putere reactiva:

1. Continuously monitor busbar voltage and reactive power
2. Capacitor switching-in allowed only when both conditions are satisfied: Busbar voltage within permitted range + system inductive reactive power exceeds switch-in threshold → relay contact closes to drive vacuum contactor to switch capacitor in.
3. When busbar voltage is too high or system becomes capacitive (reverse reactive power flow) exceeding switch-out threshold → relay contact opens to switch capacitor off.

Switching algorithms:

Equal-capacity banks: Balanced cyclic switching, equalize operation count of each bank to extend service life

Unequal-capacity banks: Adaptive combined switching, select optimal capacity combination according to reactive magnitude for higher compensation precision and avoid oscillation

Any faulty/maintenance capacitor bank is automatically masked; remaining banks keep automatic operation.

III. Blocking Protection Principle (Safety Core)

All models have multi-layer blocking. Once blocking condition triggers, capacitor switching-in is prohibited immediately; already-connected capacitors will be tripped if needed:

1. Overvoltage Blocking: Busbar voltage＞upper limit → block switching-in and trip capacitors to avoid capacitor overvoltage damage.
2. Undervoltage Blocking: Busbar voltage＜lower limit → prohibit capacitor switching-in; switching capacitors under low voltage may amplify resonance risk.
3. Switch Position Blocking: When incoming/bus coupler switch opens, trip capacitors on this section and suspend automatic control.
4. Hardware Watchdog & Self-diagnosis: On CPU crash, hardware circuit blocks all relay outputs directly to prevent false trip/close. Detect capacitor fail-to-open / fail-to-close, trigger alarm and isolate that bank.
5. Switching Delay: Fixed waiting time after each action (10~30s), prevent cyclic switching oscillation caused by short-term grid fluctuations.
6. Three Operation Modes
7. Moda auto: Controller samples, judges and executes automatic switching / tap regulation independently (normal running mode).
8. Local Manual: Manual capacitor switching / tap raise-lower via panel keys, auto logic suspended, for commissioning and maintenance.
9. Telecomanda: Backstage sends remote switch commands via Modbus; local auto logic exits under remote mode, protection blocking remains active.
10. Series T (DWK3‑110TC Tap-regulated compensation, different principle)

Series T is not conventional stepwise capacitor switching. It adjusts taps of on-load autotransformer connected in series before capacitors, changing voltage across capacitors to continuously and smoothly vary reactive output. Capacitors do not need frequent switching, resulting in lower impact and longer service life.