As the core equipment of the generator set, the overspeed protection system of the steam turbine is the key barrier to ensure the safety of the unit. The core goal of overspeed protection is to prevent the rotor components from being damaged or the runaway accident caused by the sharp increase of centrifugal force when the speed exceeds the rated value.

OPC overspeed protection suppresses the speed rise by quickly closing the regulating valve. The solenoid control valve group JZ-PK-002 is the core execution unit of OPC overspeed protection, and its control logic directly determines the rapid response capability of the regulating valve and the system reliability.

I. Structure and working principle of JZ-PK-002 solenoid valve set

Solenoid valve set JZ-PK-002 adopts a two-stage valve body design, integrating electromagnetic drive and hydraulic control functions, and mainly includes the following core components:

First-stage solenoid valve: a small-diameter valve core controlled by a coil, used to trigger the action of the second-stage valve;

Second-stage hydraulic valve: realize the pressure relief control of the OPC main pipe through oil pressure changes;

Redundant parallel circuit: usually equipped with double solenoid valves, any valve action can trigger protection to avoid single point failure.

Action logic:

During normal operation: the solenoid valve is in a power-off state, the first-stage valve is closed, the OPC main pipe oil pressure is maintained stable through the throttle hole, the valve oil motor piston lower chamber is adjusted to establish oil pressure, and the valve remains open.

When overspeed or load shedding: when the speed reaches 103% or the generator main switch trips, the solenoid valve is powered on. After the first-stage valve is opened, the oil pressure on the upper part of the second-stage valve is released through the oil drain channel, the OPC main pipe oil pressure drops rapidly, triggering the unloading valve to open, and the regulating valve is closed within 0.15 seconds.

This design achieves millisecond response through the coordinated control of electromagnetic and hydraulic pressure, which is significantly better than traditional mechanical protection systems.

II. Key technical points of integrated control logic

The integrated control logic of JZ-PK-002 OPC solenoid valve unit needs to be deeply linked with DEH, ETS and other systems, specifically including the following levels:

1. Signal acquisition and processing

Speed ​​signal three-out-of-two logic: The DEH system collects three-way speed signals through a magnetic resistance probe, and after processing by the speed measurement card, uses a “three-out-of-two” voting mechanism to determine the overspeed state to avoid false operation or refusal to operate.

Load shedding detection: Combine the generator power signal (three-out-of-two), the main circuit breaker status and the steam pressure parameters to predict the risk of load mutation and trigger the OPC action in advance.

2. Action triggering and execution

Dual protection of hard-wired circuit and soft logic: After the DEH controller detects overspeed or load shedding, it not only closes the regulating valve through soft logic instructions, but also sends a signal to the hard-wired circuit to directly drive the solenoid valve to operate, forming a “electronic + hydraulic” dual protection.

Delay reset mechanism: When the speed drops below 102%, the solenoid valve automatically resets, the OPC oil pressure is rebuilt, and the regulating valve is gradually opened to avoid secondary overspeed.

3. Redundancy design and reliability verification

Solenoid valve parallel redundancy: Dual solenoid valves are independently powered, and any failure in any circuit does not affect the system function, and online testing is performed regularly through the OPC test key switch (only in the speed control stage).

Oil circuit isolation design: The OPC oil circuit is physically isolated from the AST (automatic shutdown protection) oil circuit to ensure that the main steam valve state is not affected when the overspeed protection is activated, and the unit is kept locked.

III. Coordination mechanism with other protection systems

The control logic of JZ-PK-002 needs to form hierarchical protection with electrical overspeed and mechanical overspeed:

Cooperation with DEH electrical overspeed: DEH overspeed (110% action) is the second layer of protection, and the safety oil is drained through the AST solenoid valve to close the main steam valve; while OPC, as the first layer of protection, only closes the regulating valve to avoid unit tripping.

Complementary with TSI overspeed: The TSI system uses an eddy current probe to independently monitor the speed. Its overspeed signal is processed by the ETS (emergency trip system) three-out-of-two logic to trigger the AST action, forming electrical redundancy with DEH overspeed.

Backup function of mechanical overspeed: When the electrical protection fails, the hammer mechanism forces pressure relief at 111%-112% speed, and cuts off all steam inlet channels through the membrane valve.

This multi-level design ensures that any single system failure will not lead to loss of protection function, which meets the extreme reliability requirements of nuclear power and supercritical units.

The OPC solenoid valve JZ-PK-002 plays the role of “first responder” in turbine overspeed protection through precise multi-level control logic. Its integrated design not only achieves rapid suppression of overspeed risks, but also reduces the false operation rate and refusal rate to a minimum through redundant mechanisms and system coordination.

When looking for high-quality, reliable steam turbine solenoid valves, YOYIK is undoubtedly a choice worth considering. The company specializes in providing a variety of power equipment including steam turbine accessories, and has won wide acclaim for its high-quality products and services. For more information or inquiries, please contact the customer service below:
E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229

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