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Gate Position Indication
In a hydroelectric power station, the wicket gate on a Francis or Kaplan turbine plays a crucial role in controlling water flow into the unit. By adjusting the gate's position, operators can change the turbine's rotation speed and the volume of electricity produced. This image shows a series of generators housed within Hoover Dam. Each generator is paired with a turbine beneath it, and water from Lake Mead is directed into these turbines to drive their respective generators.
The wicket gate consists of adjustable guide vanes encircling the turbine, directing the water flow towards the runner. The runner is directly connected to the generator shaft. These cross-sectional views depict the wicket gate (in yellow) at its minimum flow setting (on the left) and at full capacity (on the right). The runner is highlighted in red.
*Originally uploaded by Stahlkocher at de.Wikipedia.*
The power output of a generator is closely linked to the head, which refers to the height of water in the reservoir. On the graph illustrating power versus head, point A represents the rated electrical power output at the standard head level, with the gate positioned at G2. At this setting, an increase in head results in more power being generated (point B), but this could potentially cause cavitation. To maintain optimal power output while ensuring safe operation (point C), the gate opening must be decreased to G1. Additionally, the gate position might be lowered further to generate less than the rated power when energy demands are low. Typically, the gate position is regulated by a governor control system, and an operator sets a gate limit.
Early hydroelectric control systems incorporated an analog gate position indicator (GPI). A precision potentiometer, often referred to as a Helipot, was mounted onto the wicket gate mechanism to provide a voltage output proportional to the gate's position. This signal supplied feedback to the governor control and was also displayed on an analog voltmeter. In certain setups, it was routed through a current transducer, generating a milliamp signal to feed a remotely located 0-1, 0-20, or 4-20 mA GPI.
Basic gate position indicators merely displayed the gate's position, while the gate limit was shown on a separate dial or meter. With this configuration, operators found it challenging to gauge the gate's position relative to its limit. The preferred approach, used by companies like Woodward Governor, involved a dual-pointer meter displaying both signals on a single dial. The black pointer on this GPI indicates the actual gate position, whereas the red pointer marks the gate limit.
The digital alternative to this meter is the Weschler Gate Position Indicator. It’s a specialized Tricolor BarGraph meter with two signal inputs—gate position and gate limit—that are simultaneously displayed in the LED bar. Operators can press the arrow button to view precise position, limit, or difference readings on the 4-digit display. Two relay outputs are available to trigger external alarms or execute control actions. The trend arrow shows the last direction of gate movement. The Weschler offers three case sizes: 4½†switchboard, 8¾†switchboard, and 8†round. A key advantage of the bargraph display is its ability to clearly indicate if the gate position surpasses the gate limit. Here, green represents the gate position, yellow the limit, and any overlap appears in red.
Modern hydro governors employ various strategies for generator control to enhance performance under fluctuating conditions. A separate digital gate position indicator, combined with a bargraph power meter, provides operators with a clear, user-friendly status update on turbine operations.
If you need assistance, don’t hesitate to reach out to Weschler. They’re always ready to help with your hydroelectric needs.
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