I. Overview

A winch, also known as a hoist, is a light and compact lifting device that uses a drum to wind up steel wire ropes or chains for lifting or pulling heavy objects. Winches can lift objects vertically or pull them horizontally or at an incline. They are primarily used for lifting and transporting materials in construction, hydraulic engineering, forestry, mining, docks, and other similar fields—such as the installation and dismantling of various large- and medium-sized concrete structures, steel structures, and mechanical equipment. The key structural features of a winch include orderly arrangement of steel wire ropes, reliable suspension and installation, and suitability for bridge, port, and road projects as well as for installing equipment in large-scale factories and mines. Essentially, a winch operates by being driven by an external force (such as an electric motor), which then, through electromagnetic brakes and mechanical locking brakes, prevents it from running freely when the power is off. After being slowed down by the motor, the winch drives a pulley that can wind up steel cables or other materials. A hoist winch is an essential piece of equipment used to transport charge materials to the top of a blast furnace for charging or to convey ore materials in inclined mine shafts. In China, small- and medium-sized blast furnaces generally adopt car-type winches as their standard charging equipment. Such winches must meet the following requirements: sufficient conveying capacity, ensuring that the charging speed meets the production demands of the blast furnace; reliable and durable operation, guaranteeing continuous blast furnace production; the ability to automate the charging process; and a simple structure that is easy to maintain.

II. Working characteristics of the hoist:

It features slow startup speed, high torque, smooth acceleration, and stable and precise stopping. The traditional speed-control method involves using a wound-rotor induction motor, in which several segments of resistance are connected in series with the rotor circuit via slip rings and carbon brushes. The speed is controlled by using contactors to switch in varying amounts of resistance. However, this method has the following drawbacks:

In series resistance speed control, the speed variation is abrupt and step-like, causing impact forces to act on the gearbox gears, sheaves, intermediate wheels, material carts, and inclined bridge rails during both acceleration and deceleration phases. This makes the equipment prone to damage, the steel wire ropes susceptible to fatigue, and leads to increased maintenance requirements and higher repair costs. The narrow speed-control range of series resistance speed control results in sudden changes in the material cart’s speed; even after deceleration, the cart still maintains a relatively high rotational speed when coming to a stop, placing stringent demands on the adjustment accuracy of brakes and limit switches. Moreover, this type of speed control easily leads to overshooting and derailment accidents, thereby disrupting production. During the start-up and deceleration of the material cart, most of the electrical energy consumed by series resistance speed control is dissipated in the resistors. When the motor voltage drops, the torque decreases, the slip rate increases, and in severe cases, the material cart may fail to start altogether, making accidents more likely to occur.

It has high energy consumption and soft mechanical characteristics at low speeds. This is because the reduction in speed is achieved by dissipating energy through external resistors connected to the rotor; the lower the speed, the softer the mechanical characteristics become, and the greater the proportion of energy dissipated in the resistors, making the system highly inefficient. Moreover, fluctuations in grid voltage significantly affect the speed.

III. Features of the PI500 Inverter

Accurate motor parameter self-learning, high speed stability accuracy, wide speed regulation range, small torque ripple at low speeds with high torque output, no downtime during temporary power outages, independent air duct design for operation in 40℃ ambient temperature, next-generation energy-saving operation, three-proof coating treatment, global safety certifications CE/TÜV, built-in adaptive PID control module, user-friendly host computer software, I/O expansion capability, integrated braking unit, support for multiple communication protocols, high-protection membrane keypad, multiple installation options—including flange mounting and detachable fan—facilitating easy installation and maintenance, plus the addition of a QUICK multi-function key and keyboard lock function option.

IV. Renovation Examples:

4.1. On-site process conditions:

At a steel plant in Jieyang City, Guangdong Province, a customer’s material-conveying elevator originally used a wound-rotor AC asynchronous motor, model YZR225M-6 (6-pole, 30 kW). This motor was powered by industrial-frequency electricity, and its speed regulation was achieved by inserting several segments of resistance into the rotor circuit via slip rings and carbon brushes. The number of resistance segments connected was controlled by contactors, which were interlocked with a cam controller and contactors themselves.

4.2. Variable Frequency Drive Retrofit Solution:

Retain the original holding brake system and remove the original control cabinet and relays.

A machine equipped with the Prolink PI500 series PI500 037G3 inverter.

In conjunction with the PB200 braking unit, the electrical energy regenerated by the motor during the winch’s descent is dissipated, preventing overvoltage faults in the machine.

Positioning is achieved through encoder and PLC control, and material cart positioning can be realized on the touch screen.

To prevent derailment and stoppage during lifting or lowering, it is essential to employ both hydraulic brakes and manual brakes for mechanical braking.

V. Application Effects:

From the perspective of post-modification operation, the results are remarkably evident. The system employs two-stage speed control: the starting frequency is set at 10 Hz, and during startup, the machine accelerates to 35 Hz as it reaches the first position. Once the machine arrives at the second position, the frequency drops back down to 10 Hz before finally coming to a complete stop. The machine’s start-up and stop processes feature minimal impact, allowing for smooth acceleration and deceleration. This reduces the shock exerted on the variable-speed gears during motor startup, making the winding hoist’s start-up, braking, acceleration, and deceleration processes smoother and faster. Consequently, load fluctuations are minimized, and the operation becomes more flexible and easier to master. Since the motor’s starting current is kept relatively low, frequent starts and stops result in reduced thermal losses and extended motor life. Moreover, the hydraulic brake and manual brake can be operated at lower speeds, which not only reduces wear on the brake pads but also prolongs their service life, thereby cutting down on maintenance time and costs. The service life of the hoist’s steel wire rope has also been significantly extended. The stopping positions are highly accurate, with both loaded and unloaded vehicles stopping at virtually identical locations. The customer’s requirement stipulates that the positional deviation must not exceed 30 centimeters. By eliminating the external starting resistor, the system’s power efficiency has been further improved, fully meeting the customer’s operational demands.