A vacuum interrupter typically consists of one fixed contact and one moving contact, a flexible bellows that allows the movement of the moving contact, and arc shields enclosed within a hermetically sealed glass, ceramic, or metal housing maintained at a high vacuum. The moving contact is connected to the external circuit via a flexible braid and is actuated by a mechanism when the device is required to open or close. Due to the atmospheric pressure that tends to close the contacts, the operating mechanism must exert sufficient force to keep the contacts open against this pressure.
Key Properties Of Contact Materials Include
- High Breaking Ability: Excellent electrical conductivity, low thermal conductivity, high heat capacity, and low hot electron emission.
- High Breakdown Voltage and Resistance to Electrical Erosion.
- Resistance to Welding.
- Low Cutoff Current Value.
- Low Gas Content, especially in copper.
Contact Design
Contacts are often shaped with slots, ridges, or grooves to improve their ability to break high currents. These geometric features generate magnetic forces on the arc column, causing the arc contact spot to move rapidly over the surface of the contact. This rapid movement reduces contact wear due to arc erosion, which can melt the contact material at the point of contact.
External Operating Mechanism
An external operating mechanism drives the moving contact, enabling the opening and closing of the connected circuit. The vacuum interrupter includes a guide sleeve to control the movement of the moving contact and protect the sealing bellows from twisting, which could significantly shorten its lifespan.
Manufacturing and Testing
Only a few manufacturers worldwide produce the contact material for vacuum interrupters. The basic raw materials, copper and chromium, are combined using an arc-melting process to form the contact material. The resulting raw parts are then processed into radial magnetic field (RMF) or axial magnetic field (AMF) contact discs, with the slotted AMF discs undergoing final deburring.
To ensure high endurance in practical applications, the bellows are subjected to regular endurance tests every three months. These tests are conducted in fully automated test cabins with travel distances adjusted to the specific type of bellows. The bellows are designed to last over 30,000 CO (close-open) operation cycles, demonstrating their robustness and reliability.
Technical Parameters
| MAIN TECHNICAL DATA | ||
| Data | Unit | Value |
| Rated Voltage | kV | 25.8 |
| Rated Current | A | 630 |
| Rated Frequency | Hz | 50/60 |
| Rated Short-duration Withstand Voltage(1min) | kV | 60 |
| Rated Lightning Impulse Withstand Voltage | kV | 150 |
| Rated Short-circuit Breaking Current | kA | 32.5 |
| Rated Short-circuit Breaking Current Breaking Times | Times | 30 |
| Rated Peak Withstand Current | kA | 32.5 |
| Rated Short-circuit Making Current | kA | 32.5 |
| Rated Short-duration Withstand Current | kA | 12.5 |
| Rated Duration of Short-circuit | s | 3 |
| Mechanical Endurance | Times | 10000 |
| Contact Closing Force | N | 50±25 |
| Force Required to hold contacts open at full stroke | N | 140±40 |
| Circuit Resistance at the Lowest Rated Contact Force | μΩ | ≤35 |
| Contact Erosion Limit | mm | 3 |
| Internal Gas Pressure | Pa | ≤1.33x10-3 |
| Mass of Moving Parts | kg | ＜0.4 |
| Storage Life | Years | 20 |
| Data for Matchable VCB | ||
| Contact Stroke | mm | 12±1 |
| Average Opening Speed | m/s | 1.2±0.1 |
| Average Closing Speed | m/s | 1.0±0.1 |
| Rated Contact Force | N | 1200±100 |
| Contact Initial Pressure | N | 850±100 |
| Contact Closing Bouncing Duration | ms | ≤2 |
| Contact Opening and Closing Non-simultaneity | ms | ≤1 |
| Contact Opening Rebound Amplitude | mm | ≤2 |
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