Design of Electrical Control System for 2×1600KN Tailrace Gate Hoist

Abstract: This paper mainly introduces the features and electrical system design of the Guanyinyan 2×1600KN bidirectional tailrace gantry crane. It focuses on the hardware and software design process of the electrical system, provides the commissioning parameters of the hoisting mechanism according to the field conditions, and gives specific solutions to common faults that are prone to occur during the commissioning of the gantry crane.

1 Introduction

Our company independently developed and designed a 2×1600kN bidirectional gantry crane for the Guanyinyan Hydropower Station. Installed on the tailrace dam top platform of the powerhouse, the 2×1600kN lifting mechanism operates with dual lifting points, using a hydraulic grab beam to open and close the tailrace maintenance gate and floodgate of the power generation system, and to lift the gate opening covers. The crane's electrical control system adopts the internationally advanced "touchscreen + PLC + frequency converter" control scheme, and the entire machine has the following advantages:

1. Large tonnage and high lifting capacity. This gantry crane has a lifting capacity of up to 3200KN and a lifting height of up to 73.5 meters, including 60 meters below the rail and 13.5 meters above the rail.
2. The trolley lifting mechanism adopts a dual-point lifting mechanism, consisting of two sets of drive devices and two sets of zigzag drum devices, to achieve multi-layer winding of the lifting mechanism.
3. The hoisting mechanism employs master-slave control technology to ensure consistency in speed and torque between the two hoisting mechanisms.
4. The machine adopts advanced touch screen monitoring technology, giving it excellent human-machine interaction and high-quality information processing capabilities.
5. By using a PLC to collect various signals and utilizing the virtual contacts inside the PLC to achieve sequential logic control of the entire machine, the number of intermediate relays and time relays in the control cabinet is greatly reduced, thereby reducing hardware failures in the electrical system and improving the reliability of system control.
6. All transmission mechanisms adopt the Yaskawa H1000 series variable frequency speed control method, with a speed ratio as high as 1:20.
7. Complete safety protection functions. In addition to the conventional protections required by the electrical control system, such as short circuit protection, overcurrent protection, undervoltage protection, phase loss protection, grounding protection, zero position protection, limit protection, overload protection, main disconnect switch, and emergency switch to disconnect the main power supply, this machine also has load protection, lifting height limit and overspeed protection.

2. Electrical System Design

The electrical system of this gantry crane mainly includes a power supply system, a hoisting mechanism control system, a trolley traveling mechanism control system, a gantry traveling mechanism control system, a hydraulic grab beam control system, a safety protection system, lighting and grounding, and a lightning protection system.

2.1 Power Supply System

The machine is powered by a cable reel, with a three-phase four-wire AC380V, 50HZ power supply. The control power supply is AC220V, provided by a dedicated transformer.

The main power supply is equipped with an isolating knife switch Q1, which can cut off all power to the machine, providing a clear disconnect point for safe maintenance. It also includes a circuit breaker QF01 for short-circuit protection only. Under normal circumstances, QF01 does not operate; the main contactor KM1 is used to connect or disconnect the main power supply. QF01 contains a shunt trip coil, controlled by the emergency stop button on the power cabinet. The shunt trip device is only used occasionally in emergency situations where the main contactor fails to disconnect the power circuit normally for some reason.

2.2 Lifting Mechanism Control System

The hoisting mechanism carries a typical potential energy load, driven by two QABP315M8A 75kW variable frequency motors. Two Yaskawa H1000 series frequency converters from Japan are used for separate drive and closed-loop control. A master-slave control system is employed between the two frequency converters to ensure consistent torque and speed between the two motors. The hoisting mechanism features various fault self-diagnosis and alarm functions, including instantaneous overcurrent protection, instantaneous power failure and undervoltage protection, grounding protection, cooling fan malfunction protection, overfrequency (overspeed) protection, contactor adhesion protection, phase loss protection, controller zero-position protection, overload protection, etc.

(1) Speed ​​pointer:

Under light load, the flow rate is 0.44–4.4 kWh/min (Q ≦ 300 kN).

Under heavy load, the output is 0.22 to 2.2 kWh/min (Q ≥ 300 kN).

(2) Speed ​​regulation method:

The system determines whether a system is under light or heavy load by checking the light and heavy load status output from the load cell and using the selector switch on the control panel. The speed is determined by the position setting of the control panel's master switch. There are five speed settings in both directions: 20%, 60%, 100%, 150%, and 200% of rated speed for light load, with the first three settings providing constant torque speed regulation and the fourth and fifth settings providing constant power speed regulation; and 10%, 20%, 40%, 70%, and 100% of rated speed for heavy load, also with constant torque speed regulation. The system uses a master switch input to the PLC, which processes the data and then outputs a switch signal to the frequency converter. The speed settings can be arbitrarily set within the frequency converter to meet different speed requirements.

(3) Operation and Protection

① Each hoisting mechanism consists of a working brake and a hydraulic safety brake. The working brake engages the high-speed shaft, and the safety brake engages the low-speed shaft. The safety brake opens immediately after the hoisting mechanism's main contactor is closed, and engages immediately after the hoisting mechanism has been inactive for 1 hour.

② When the frequency converter or braking unit fails, a pair of normally open contacts of each output fault inside the device will be activated to stop the device and trigger an alarm.

(4) The hoisting mechanism is equipped with a comprehensive protection device based on load and height. When the load at the lifting point reaches 90% of the rated lifting capacity, an automatic warning alarm signal is issued; when it reaches 105% of the rated lifting capacity, a delayed alarm and power cut-off occur; when it reaches 110% of the rated lifting capacity, an immediate alarm and power cut-off occur (operation continues even during descent); when the load on the lifting device is zero, an underload warning signal is given; when the hoisting mechanism reaches its limit position, the power supply in the corresponding direction is automatically cut off and an alarm is triggered. The hoisting mechanism is equipped with mechanical limit switches, which automatically cut off the power supply in the corresponding direction when the hook reaches its upper or lower limit position, stopping the mechanism's operation. This, together with the comprehensive protection device, constitutes a dual electromechanical protection system.

2.3 Control System for Trolley Traveling Mechanism

The trolley mechanism has a typical displacement load, driven by four AWV90S-4-B 1.1kW variable frequency motors, using Yaskawa H1000 series frequency converters from Japan, with open-loop control.

(1) Speed ​​pointer:

Operating speed: 0.2~2m/min

(2) Speed ​​regulation method:

The speed is determined by the position of the master control switch on the driver's cab control panel. There are five speed settings each for forward and reverse, corresponding to 10%, 30%, 50%, 70%, and 100% of the rated speed. The system uses a master control position switch input to the PLC, which processes the data and then outputs a switch signal to the frequency converter. The speed setting can be arbitrarily set within the frequency converter to meet different speed requirements.

(3) Operation and Protection

① The mechanism is equipped with two hydraulic electric rail clamps. The trolley mechanism can only operate when the rail clamps are open and the external wind speed does not exceed 20m/s.

② Each motor is equipped with thermal overload protection. In the event of a fault in the frequency converter or braking unit, a pair of normally open contacts on each output fault inside the device will activate the fault stop and trigger an alarm.

2.4 Control System for the Tractor Traveling Mechanism

The trolley mechanism has a typical displacement load, driven by eight AWV132S-4-B5.5kW variable frequency motors, using Yaskawa H1000 series frequency converters from Japan, with open-loop control.

(1) Speed ​​pointer:

Operating speed: 2～20m/min

(2) Speed ​​regulation method:

The speed is determined by the position of the master switch on the driver's cab control panel. There are five positions each for left and right, corresponding to 10%, 30%, 50%, 70%, and 100% of the rated speed. The system uses master position switch input to the PLC, which processes the data and then outputs a switch signal to the frequency converter. The speed can be arbitrarily set within the frequency converter to meet different speed requirements.

(3) Operation and Protection

① The mechanism is equipped with two hydraulic electric rail clamps, one anemometer and two sets of anchoring devices. The trolley mechanism can only operate when the rail clamps are open, the external wind speed is less than 20m/s and the anchoring devices are open.

② Each motor is equipped with thermal overload protection. In the event of a fault in the frequency converter or braking unit, a pair of normally open contacts on each output fault inside the device will activate the fault stop and trigger an alarm.

2.5 Hydraulic grab beam control system

The hydraulic automatic beam attachment and release system utilizes a magnetically coupled cable reel for power supply and signal detection. The cable winding and unwinding speed is synchronized with the gantry crane's lifting speed. The automatic beam attachment and release mechanism is controlled by an oil pump motor and a solenoid directional valve installed in the hydraulic pump station. Detection signals are provided by six proximity switches distributed across various locations on the beam. Two are for alignment, two for pin insertion, and two for pin release.

2.6 Lighting, grounding, and lightning protection systems

This machine is equipped with a separate lighting system, which is powered by a dedicated lighting transformer.

Regarding the grounding system, this machine is equipped with a dedicated grounding wire. The steel structure of the driver's cab is reliably connected to the main body of the machine, ensuring that the grounding resistance at any point on the steel structure of the machine does not exceed 4 ohms.

The machine is also equipped with a surge protector, which can effectively protect personnel and the door machine's electronic equipment from lightning strikes.

3. Design of Electrical Control System

3.1 Hardware Design of Electrical Control

The S7-200 series PLC excels in the following aspects:

① Extremely high reliability; ② Extremely rich instruction set; ③ Easy to learn; ④ Convenient operation; ⑤ Rich built-in integrated functions; ⑥ Real-time characteristics; ⑦ Powerful communication capabilities; ⑧ Rich expansion modules.

Based on the above advantages of S7-200PLC, this bidirectional gantry crane uses S7-200PLC as the control core. The specific hardware composition is shown in Figure 1 below.

The entire PLC control system consists of a CPU226, two digital input/output modules EM223, one digital input module EM221, and one analog input/output module EM235. The CPU226 is the central processing unit, processing various externally input information. The digital input/output modules receive various external fault signals, operating status signals of each mechanism, input signals from the control panel, and output control commands to each mechanism to complete the start-up, operation, and braking of each operating mechanism. The analog module EM235 mainly receives high-order analog signals. (Figure 1: PLC Hardware Composition)

The system transmits analog signals for load, wind speed, and other parameters. These signals are processed by the PLC module and then transmitted via the MPI network to the touchscreen in the operator's cab, allowing the operator to monitor the gantry crane's overall operating status in real time.

3.2 Software Design of Electrical Control System

Since this gantry crane uses the S7-200 as the core of its control system, the system is programmed using Step7Microwin4.0 programming software. The specific program control flow is shown in Figure 2 below.

Figure 2 Program control flowchart

4. Adjustment of the lifting mechanism

Before setting the parameters of the hoisting mechanism's frequency converter, the hoisting motor needs to undergo rotational self-learning. If the motor cannot be disconnected from the load, the hoisting motor should undergo stop-type self-learning.

After the frequency converter has completed self-learning, before performing master-slave debugging, the synchronous rigid shafts of the two hoisting mechanisms need to be connected. The parameters of the hoisting mechanism frequency converter are shown in Table 1 below.

Table 1 Parameters of the Hoisting Mechanism Inverter

5 Common Troubleshooting Methods

This article mainly addresses some common and easily occurring faults during the commissioning of hoisting mechanisms and lists the following solutions, as shown in Table 2.

Table 2 Common Faults and Solutions

6. Conclusion After a long period of research and development and debugging, the electrical control system independently designed by our unit has been successfully applied to the 2×1600KN bidirectional tailrace gantry cranes of the Guanyinyan Hydropower Station, as shown in Figure 3. Field tests have shown that the gantry cranes operate smoothly overall, with minimal start-up and braking impact, receiving unanimous praise from the client.