What is a GGD-type fixed low-voltage switchgear?
The GGDtype fixed Low-Voltage Switchgear is an AC low-voltage distribution equipment with a fixed structure, suitable for use in power distribution systems with AC 50Hz, rated voltage of 380V, and rated current up to 3150A in power plants, substations, factories, mines, and other power users. It is widely used due to its simple structure, low cost, and convenient maintenance. However, there are significant differences between its fixed design and the modular and interchangeable design of drawer-type switchgear.
Overview of GGD Type Fixed Low-Voltage Switch Cabinet
- Definition and purpose
Definition: The GGDtype fixed low-voltage switchgear is a complete set of Power Distribution Equipment used indoors. The main electrical components inside the cabinet (such as circuit breakers, contactors, transformers, etc.) are installed in a fixed manner and cannot be withdrawn.
Application Scenario: Primarily used in AC 50Hz, rated voltage 380V distribution systems in power plants, substations, factories, mines, enterprises, and civil buildings, serving as a means for power conversion, distribution, and control of power, lighting, and distribution equipment.
- Analysis of model meaning
The letter G stands for fixed type (installation method), G for cabinet type (structural form), and D for electric power use (application field).
Complete model examples: GGD1, GGD2, and GGD3, each corresponding to a different interrupting capacity level (e.g., GGD1 is 15kA, GGD2 is 30kA, and GGD3 is 50kA).
Structural characteristics and composition
- Basic structure ·
Cabinet body: It is made of cold-rolled steel plates or aluminum-zinc-coated steel plates, bent and welded together, providing high mechanical strength and protective capability.
Busbar system: The horizontal busbars (main busbars) on the top of the cabinet are arranged in a continuous manner, supplying power to each unit through T-connection. The busbar material is usually copper bar, and the current-carrying capacity is designed according to the rated current.
Fixed installation: All components (such as circuit breakers, contactors, fuses, transformers, etc.) are directly mounted on the mounting board inside the cabinet through fixed brackets and bolts, and cannot be withdrawn and replaced as a whole like a drawer cabinet.
- Main internal components ·
Incoming circuit breaker: Typically, it is a frame-type circuit breaker (ACB) or a molded case circuit breaker (MCCB), used for making and breaking the main circuit.
Outgoing circuit: It is directly connected to the load through a cable, which enters from the lower part of the cabinet. Secondary components such as current transformers, voltage transformers, and lightning arresters can be installed inside the cabinet.
Secondary control and protection: Secondary devices such as instruments, microcomputer protection devices, buttons, indicator lights, and changeover switches can be installed on the cabinet door panel, and secondary wiring terminal blocks are arranged inside the cabinet.
Earthing switch: Some circuits are equipped with earthing switches, which are used to ground the main circuit during maintenance to ensure safety. Additionally, there is a mechanical interlock between the earthing switch and the circuit breaker to prevent misoperation.
3. Fixed type vs drawer type comparison
| Comparison item | GGD fixed type | |
| Installation method | The components are fixed and installed inside the cabinet | The components are installed in a withdrawable drawer unit |
| Maintenance convenience | The door needs to be opened for maintenance after the power is cut off, and replacement is quite troublesome | The drawer can be pulled out, and some circuits can be replaced without power outage |
| interchangeability | Circuits cannot be interchanged | Drawers of the same specification are interchangeable |
| cost | lower | higher |
| Applicable scenarios | A place with stable load and fewer circuits | Places with multiple circuits and frequent switching needs |
| typical model | GGD | GCK、GCS、MNS |
In low-voltage distribution cabinets, GGD represents an earlier and classic fixed design, while GCK, GCS, MNS, etc. are representatives of drawer-type (withdrawable) switch cabinets, each with its own advantages and disadvantages.
Technical parameters and standards
- Main electrical parameters
Rated voltage: AC 380V (main circuit), 220V (control circuit) .
Rated frequency: 50Hz .
Rated current: The incoming cabinet can reach up to 3150A, and the feeder cabinet varies from 100A to 630A depending on the circuit configuration.
Rated short-circuit withstand current: Usually divided into three levels: 15kA (GGD1), 30kA (GGD2), and 50kA (GGD3).
Protection level: Generally IP30 (protection against solid foreign objects larger than 2.5mm), which can be improved to IP40 according to requirements.
- Executive standards
Main standards: GB/T 7251 "Low-voltage Switchgear and Controlgear Assemblies", IEC 61439 series.
Design features: Complies with the typical design requirements of the State Grid Corporation of China, and is widely used in the fields of power, petrochemical, metallurgy, construction, etc.
Precautions for application and selection
- Typical application scenarios
Industrial and mining enterprises' distribution rooms: Serving as the main power distribution cabinet or sub-distribution cabinet for workshop power.
Civil building substation: Used for power distribution to lighting, air conditioning, elevators, etc. on floors.
Power plant auxiliary power system: Serving as a low-voltage auxiliary power distribution device.
- Selection key points.
Current and breaking capacity: Select GGD1/2/3 grades according to the system's short-circuit capacity to ensure that the switchgear can withstand short-circuit currents.
Number and layout of circuits: Due to limited space within the fixed cabinet, it is necessary to rationally plan the units such as incoming lines, outgoing lines, bus couplers, and capacitance compensation.
Environmental adaptability: The standard model is suitable for indoor dry environments, if used in damp or dusty locations, the protection level needs to be enhanced or an anti-corrosion treated cabinet body should be selected.
Brand and quality: Pay attention to the cabinet material (such as aluminum-zinc coated steel plates are superior to cold-rolled steel plates), copper bar specifications, and component brand (such as Schneider, ABB, Chint, etc.), to ensure reliability.
Distinction from other commonly used low-voltage cabinets
| model | structural type | Maximum rated current | characteristic | Applicable scenarios |
| fixed type | 3150A | Low cost, simple maintenance, and average space utilization | Small and medium-sized power distribution system, stable load | |
| drawer-type | 4000A | Drawers are interchangeable, easy to maintain, and highly reliable | Large distribution room, frequent operations | |
| drawer-type | 4000A | High degree of modularity, with a protection level option of IP54 | Places with high requirements for continuous power supply | |
| MNS | drawer-type | 5000A | Compact structure, suitable for high cabinets, intelligent integration | Large-scale industries, data centers |
In the selection of low-voltage distribution cabinets, GGD remains the first choice for many small and medium-sized projects due to its economy.While scenarios requiring high reliability and uninterrupted power maintenance often adopt drawer-type cabinets.
Maintenance and safety precautions
Power outage operation: During maintenance of fixed cabinets, the incoming power supply must be cut off, and the door can only be opened for operation after confirming that there is no power.
Grounding and Interlocking: Ensure reliable mechanical interlocking between the grounding switch and the circuit breaker to prevent closing the grounding switch when it is live or closing the circuit breaker by mistake.
Regular inspection: Check the busbar connections for any signs of heating or oxidation,inspect the number of operations of the circuit breaker,clean the dust accumulated inside the cabinet,test the insulation of the secondary circuit.
Heat dissipation management: When the rated current is relatively high, a cabinet top fan or ventilation louvers can be installed to prevent excessive temperature rise inside the cabinet.
