With the development of modern electronic technology, high-voltage and high-power variable frequency speed control devices have become increasingly sophisticated. The high-voltage problem that was previously difficult to solve has been well solved by connecting devices or units in series.
The Ipower series high-voltage frequency converter is an AC-DC-AC voltage source converter with a multi-unit series structure. It achieves sinusoidal input and output voltage and current waveforms through multiple superposition technology, effectively controlling harmonics and reducing pollution to the power grid and load. It is an environmentally friendly high-voltage frequency converter that does not require filters. Simultaneously, it has complete protection devices and measures to protect the frequency converter and load, eliminating and avoiding losses caused by various complex operating conditions, thus creating greater benefits for users.
1. Incoming Line Protection: Incoming line protection covers the user's incoming line and the frequency converter, including lightning protection, grounding protection, phase loss protection, reverse phase protection, imbalance protection, overvoltage protection, transformer protection, etc. These protection devices are generally installed at the input end of the frequency converter. Before operating the frequency converter, it must be ensured that the incoming line protection is working properly.
2. Lightning Protection: Lightning protection is achieved through surge arresters installed in bypass cabinets or at the input terminals of the frequency converter. A surge arrester is an electrical device that can release the energy of lightning or, simultaneously, the overvoltage energy during power system operation, protecting electrical equipment from transient overvoltage hazards. It can also interrupt follow current to prevent system grounding short circuits. The surge arrester is connected between the frequency converter's input line and ground, in parallel with the protected frequency converter. When the overvoltage value reaches the specified operating voltage, the surge arrester immediately trips, allowing charge to flow, limiting the overvoltage amplitude, and protecting the equipment insulation. After the voltage value returns to normal, the surge arrester quickly returns to its original state to ensure normal system operation and prevent damage from lightning strikes.
3. Ground Fault Protection: This is achieved by installing a zero-sequence current transformer at the inverter's input terminal. The principle of zero-sequence current protection is based on Kirchhoff's current law: the algebraic sum of the complex currents flowing into any node in a circuit equals zero. Under normal conditions of the line and electrical equipment, the vector sum of the currents in each phase is zero. Therefore, the secondary winding of the zero-sequence current transformer has no signal output, and the actuator does not operate. When a ground fault occurs in a phase, the vector sum of the currents in each phase is not zero. The fault current induces magnetic flux in the toroidal core of the zero-sequence current transformer, generating an induced voltage on the secondary side of the transformer. This voltage is fed back to the main monitoring box, which then issues a protection command, thus achieving the purpose of ground fault protection.
4. Overvoltage Protection: Phase loss, phase reversal, unbalance protection, and overvoltage protection. Phase loss, phase reversal, and unbalance protection, as well as overvoltage protection, are primarily achieved by the inverter's input voltage feedback board or voltage transformer acquiring the input voltage, and then the CPU board performing calculations to determine if there is a phase loss, phase reversal, input voltage imbalance, or overvoltage. This is because input phase loss, phase reversal, voltage imbalance, or overvoltage can easily cause transformer burnout, power unit damage, or motor reverse rotation.
5. Transformer Protection: The Ipower series high-voltage frequency converter consists of three main parts: a transformer cabinet, a power unit cabinet, and a control cabinet. The transformer is a split-type dry-type transformer that converts high-voltage AC power into a series of low-voltage phases at different angles to power the power units. The transformer can only be cooled by air cooling; therefore, transformer protection primarily relies on temperature control to prevent overheating and coil burnout. Temperature probes are placed in the three-phase coils of the transformer, with one end connected to a temperature control device. This device automatically sets the temperature for the transformer's bottom fan to start, alarm, and trip, while simultaneously displaying the temperature of each phase coil. If the temperature reaches the alarm or trip threshold, the temperature controller sends a signal to the PLC, displaying the alarm information on the user interface. The PLC then initiates alarm or trip protection.
6. Outgoing Line Protection: The outgoing line protection of the Ipower series high-voltage frequency converter is to protect the output side of the frequency converter and the load, including output overvoltage protection, output overcurrent protection, output short circuit protection, motor over-temperature protection, etc.
7. Output overvoltage: Output overvoltage protection is achieved by sampling the output voltage through the output side voltage sampling board. If the output voltage is too high, the system will automatically alarm.
8. Output overcurrent: Output overcurrent protection is determined by comparing the output current collected by the Hall effect sensor to determine whether an overcurrent has occurred.
9. Output Short Circuit: A protective measure taken when a short circuit fault occurs between phases of the motor stator winding and its leads. If the frequency converter detects an output short circuit, it will immediately block the power unit and stop operation.
