The JL-400 power protection relay is suitable for protection of power distribution systems installed in cabinets, such as distribution cabinets, distribution boxes, electrical control boxes, machine tools, and other equipment. It can replace similar products from Siemens, Schneider, Gyllenhaal, and Omron. It not only boasts superior performance but also offers excellent cost-effectiveness.
Functional characteristics of phase loss and phase sequence relays
High precision: It adopts a powerful microprocessor chip, especially AC sampling technology, with a voltage measurement accuracy of ±1%. It can display the phase voltage values of the three-phase power supply separately, which is equivalent to the function of a three-phase digital voltmeter.
Wide power supply frequency: Applicable to 45～65HZ, ensuring global compatibility (cannot be used in inverter output circuits). Wide power supply voltage: Applicable to phase voltage 150～300V (line voltage 260～520V), greatly reducing the specifications of phase failure and phase sequence relays, making it easier for users to select and reducing spare parts costs.
High reliability: It adopts a unique three-phase power supply technology, which can ensure the normal operation of protection, alarm and display functions even in the case of extremely low voltage or even phase loss.
Neutral wire breakage protection: Adopting an original technical solution, it provides dual protection against the extremely dangerous neutral wire breakage fault.
Independent normally open and normally closed outputs: Employing high-power dual-group contact relays, it can independently control devices of different voltage levels, making it more widely applicable.
Intuitive display: It adopts a dedicated wide-temperature, high-definition Chinese LCD display. During normal operation, it displays the phase voltage values of the three-phase power supply; when a fault occurs, it directly displays the cause of the fault in Chinese, and can simultaneously indicate which phase is faulty and the voltage value at the time of the fault. It is very intuitive and easy to quickly determine the cause and location of the fault.
Fault Recording: Employing non-volatile storage technology, faults are recorded when overvoltage, undervoltage, phase loss, imbalance, or phase sequence faults occur. Even if the product is completely powered off, it can still remember fault information for easy fault retrieval. It can remember the three most recent fault records.
Easy installation: The base adopts a guide rail design with two M4 screw holes, which can be installed with HT35 guide rails or fixed with M4 screws, providing two installation methods for greater flexibility and convenience.
Phase loss and phase sequence protection circuit
Currently, in low-voltage power distribution systems in factories, protection devices for motors and high-power three-phase equipment are widely used. These devices typically only have overcurrent and short-circuit protection relays. Various books and magazines have previously published articles on motor protectors, including induced current type, temperature sensing type, and zero-point drift type. When a phase is lost, the lost phase conductor is not 0V, but rather has a voltage ranging from 127 to 180V. This is mainly because the internal circuits of the three-phase equipment on the main line are connected in pairs, and the same applies to motors. The phase loss protector introduced here can be used in both main power grids and motors. Its functions include protection against abnormal phase sequence, phase reversal, phase loss, and large three-phase voltage imbalance (the allowable voltage fluctuation range is 90%Ue to 110%Ue; protection is provided even if one or two phases are lost. It can reliably operate when the three-phase voltage asymmetry is ≥13%).
The circuit diagram of the phase failure protector is shown in the figure below.
The working principle is explained as follows:
A, B, and C are connected in parallel to phases A, B, and C of a 380V AC power grid. A phase-shifting circuit composed of resistors R1, R4, R2, R5, C1, R3, R6, R16, R17, and C6 is used. Under normal voltage conditions with correct phase sequence and no phase loss, the vector voltage at the rectifier input (composed of diodes D5, D7, D8, and D13) is small, resulting in a low rectified voltage. When a phase is lost or the phase sequence is incorrect, the output voltage momentarily rises to approximately 13V. After filtering by V4 and current limiting by R8, the voltage is regulated by D9, stepped down and matched by R9, R10, and R11, and then filtered by C5. The voltage is then input to pin ② of the comparator LM358 via current-limiting resistor R12 as the detected signal voltage.
Power is supplied by a 380V/13V transformer connected to phases A and B. After filtering by C2, current limiting and voltage reduction by R7, voltage regulation by D6, and further filtering out transient waves by C3, one path powers the LM358, while the other path generates a 5-7V reference voltage through voltage division by R13 and R14. This reference voltage is input to pin 3 of the LM358. The LM358 voltage comparator outputs a comparison judgment signal. After voltage regulation and limiting circuitry (C7 and D14 raise the threshold voltage to prevent malfunction due to single pulse voltage interference), the relay is driven by O1. If the phase sequence is correct and there is no phase loss when ABC is connected to the power grid, JDQ1 will engage. If there is a phase loss or incorrect phase sequence, JDQ1 will immediately release, and the main line relay will de-energize and release.
The original external wiring had the following drawback: when the contacts of the main line relay were faulty or burned out by electrical sparks, the main line relay could still remain connected. The author has improved this design, as shown in the figure. This eliminates the problem of the main relay failing to disengage due to burnt-out relay contacts.
