Ningguo Kingcool Import and Export Co., Ltd is a China-based Refrigeration Parts-Voltage Protector Manufacturers and one-stop supplier of HVAC and appliance parts. We produce metalized polypropylene film capacitors on high-precision slitting and winding lines, and we supply voltage protectors, capacitors, contactors, relays and installation accessories for refrigeration, air-conditioning and cold-chain equipment.
Our range addresses the two voltage conditions that damage refrigeration compressors: deep startup sags and sustained running overvoltages. We configure protection thresholds, time delays and input filtering around the compressor, the grid and the control panel, then deliver matched components from a single source.
What We Supply in the Voltage Protector Range
Voltage protectors sit on the incoming supply of condensing units, cold rooms, display cabinets and packaged air-conditioning equipment. They monitor phase voltage and disconnect the compressor contactor when the supply moves outside a safe window, then reconnect after a set delay once the supply recovers.
We supply protectors as standalone units and as part of a coordinated protection set that includes suppression capacitors, contactors, overload relays and terminal accessories. Because we manufacture the capacitor element in-house, the filtering and hold-up components that keep a protector stable during transients and brief sags come from the same production and testing process.
Protection Functions and Typical Settings
The table below shows the protection functions we configure and the setting ranges we work with. Final values are set against the compressor voltage tolerance curve, the measured startup sag and the local grid quality.
| Protection Function | Typical Threshold | Time Delay | Application Purpose |
|---|---|---|---|
| Undervoltage (sag avoidance) | 65–75% of nominal | 0.5–2.0 s | Rides through normal startup sags; trips on persistent brownout |
| Severe undervoltage (locked rotor) | 50–55% of nominal | 0.1–0.3 s | Stops operation at voltages too low to accelerate the motor |
| Overvoltage (sustained) | 110–115% of nominal | 2–5 s | Ignores switching transients; protects winding insulation |
| Severe overvoltage | 125–130% of nominal | 0.05–0.1 s | Fast trip on neutral failure or severe grid fault |
| Voltage unbalance (three-phase) | Negative sequence above 2% | 1–3 s | Protects rotor bars against phase loss and unbalanced loads |
Matching the Protector to the Compressor
Single-phase hermetic compressors up to about 5 HP usually need an undervoltage trip near 70% with a 2-second delay and an overvoltage trip near 115% with a 5-second delay. That window passes the 300–400 ms startup sag typical of these units while still catching a real supply fault.
Three-phase semi-hermetic and scroll compressors from about 10 HP upward benefit from two-stage undervoltage protection: a warning stage near 75% with a 1-second delay and an immediate trip near 60% with a 0.2-second delay. Overvoltage is commonly set near 110% with a 3-second delay.
- Inverter-driven compressors regulate their own DC bus, so the protector is set on the AC input side with wider thresholds and longer delays.
- Weak-grid regions in the Middle East, Africa and Southeast Asia often need a raised undervoltage threshold combined with a longer delay.
- Settings must stay narrower than the compressor tolerance curve but wider than normal supply disturbances.
Capacitors That Keep Protection Stable
Electronic sensing circuits in voltage protectors can react to high-frequency spikes from contactor opening or nearby variable-frequency drives. A metalized polypropylene film capacitor across the input terminals filters those spikes so the protector responds to fundamental 50/60 Hz voltage changes rather than noise.
During severe sags the protector's internal supply can drop out and cause relay chatter. An energy-storage capacitor on the DC rail holds logic power through the dip, so the unit keeps its decision state instead of cycling the compressor contactor.
We produce these capacitors on automated high-precision slitting and winding equipment with real-time testing during production. Annual capacity reaches 10 million metalized film capacitors, exported to more than a dozen countries across the Middle East, Africa, South America and Southeast Asia.
Where Our Range Fits in the Refrigeration System
Voltage protection is one part of a coordinated electrical package. We supply the surrounding components so a condensing unit, cold room or service project can be equipped from one order.
Voltage Protector
Supply monitoring and trip logic for compressors and condensing units, with adjustable thresholds and delays.
Capacitor
Metalized polypropylene film capacitors for input filtering, hold-up storage and motor-run duty.
Contactor & Transformer
Switching and control-supply components that pair with the protector in the compressor circuit.
Relay & Overload & Delay Timer
Overload and timing devices that complete the compressor protection chain.
Configuration Options
- Undervoltage setting range of roughly 50–90% and overvoltage range of roughly 110–140% of nominal.
- Adjustable time delays from about 0.1 to 10 seconds, set by digital potentiometer or DIP switch.
- Single-phase and three-phase versions, with unbalance monitoring on three-phase units.
- Temperature-compensated timing circuits for cold-room and rooftop condensing-unit environments.
- Microcontroller-based digital versions with crystal-oscillator timebases where tighter delay accuracy is required.
- Factory pre-setting and custom label marking so units arrive ready for installation.
Installation, Commissioning and Maintenance
Protectors mount in the control panel or on the unit frame with standard terminal connections. We supply pre-wired terminal blocks and mounting accessories so the device integrates with existing panels without custom fabrication.
- Record the actual startup sag with a recording multimeter or power analyzer across at least ten consecutive starts.
- Set the undervoltage delay 10–20% longer than the measured sag duration.
- Verify overvoltage response with a variable autotransformer and confirm the trip point and delay.
- Document all thresholds and delays for each unit and keep them with the panel schedule.
Routine maintenance is limited to checking terminal torque, confirming the display or indicator state and re-verifying settings after any panel modification. Spare units and replacement capacitors are available as separate line items so service teams can hold stock without ordering complete assemblies.
Quality Control and Documentation
Our capacitor production runs on automated slitting and winding equipment with real-time monitoring during the process, and finished goods pass through testing equipment before packing. Automated warehousing and logistics systems manage raw materials, semi-finished and finished stock.
For voltage protector orders we can supply setting records, delay accuracy verification at temperature endpoints and label marking that matches the delivered configuration. Documentation is prepared per order so the panel builder or service contractor receives the settings that were actually tested.
Information We Use to Configure Your Solution
| Project Input | Why We Need It |
|---|---|
| Compressor model, rated power and supply voltage | Sets the protection window against the compressor tolerance curve |
| Measured startup sag depth and duration | Prevents nuisance trips during normal starting |
| Grid quality and known disturbance patterns | Determines whether thresholds or delays need widening |
| Panel layout, terminal type and mounting position | Confirms mechanical fit and wiring arrangement |
| Required delay accuracy and operating temperature range | Selects analog or microcontroller-based timing |
| Quantity, packing and delivery scope | Defines the quotation and shipment structure |
Frequently Asked Questions
Can you supply voltage protectors with custom thresholds and delays?
Yes. We offer adjustable undervoltage and overvoltage settings with delays from about 0.1 to 10 seconds. Our engineering team can pre-set parameters at the factory based on your compressor startup profile and grid conditions, and mark each unit with its delivered settings.
How stable is the time delay across refrigeration temperature ranges?
We source protectors with temperature-compensated timing circuits using low-drift RC oscillators, and our testing equipment verifies delay accuracy at temperature endpoints. For tighter control we offer microcontroller-based digital protectors with crystal-oscillator timebases for walk-in freezer and rooftop condensing-unit applications.
Do you support EMI filtering when integrating a protector into an existing panel?
We do. Our application engineers advise on pairing metalized polypropylene film capacitors with the protector input, including X-class line-to-line and Y-class line-to-ground arrangements, to suppress drive-induced spikes without slowing the protector response.
Which applications use your voltage protectors most often?
They are used on condensing units, cold rooms, display cabinets, packaged air-conditioning equipment and service projects where supply quality is variable. We also supply them alongside Refrigeration Parts and installation accessories for complete project kits.
What is the delivery scope for a voltage protector order?
Orders can include the protector, matched suppression and hold-up capacitors, terminal blocks, mounting accessories and setting documentation. Packing and shipment structure are confirmed against the quantity and destination on the order.
