Last updated on September 3rd, 2026 at 11:30 am
Gate Position is a critical parameter in hydroelectric power production. The output power of a hydroelectric generating station is regulated by adjusting the flow of water into the facility’s turbines.
The wicket gate on a Francis or Kaplan turbine controls water flow into the unit. The gate position is adjusted to provide the flow rate needed to maintain a constant, synchronous generator speed as the electrical load changes. This photo shows a row of generators inside Hoover Dam. A turbine is mounted below each generator and water from Lake Mead is funneled into each turbine to turn its generator.
The wicket gate is a set of adjustable guide vanes surrounding the turbine that directs the water flow into the runner. The runner is connected to the generator shaft. These cut-away views show the wicket gate (yellow) at minimum flow setting (left) and at full flow (right). The runner is shown in red.
Originally uploaded by Stahlkocher at de.Wikipedia.
Generator Control
Generator output power is a function of flow rate and head (the height of water column above the turbine). On the graph of power vs head, point A is the rated electrical power output at rated head, with gate position G2. At this gate opening, a higher head produces more power (point B) and risks causing cavitation. To maintain rated power output and safe operation (point C), the gate opening must be reduced to G1. The gate position may also be lowered to produce less than rated power when demand is low. Typically, the gate position is adjusted by a governor control and a gate limit is set by an operator.
Legacy Gate Position Indicators
Early hydro controls included an analog gate position indicator (GPI). A precision potentiometer (aka Helipot) mounted to the wicket gate mechanism provided a voltage output proportional to position. This signal gave gate feedback to the governor control and was also displayed on an analog voltmeter. In some systems, it was routed through a current transducer that produced a milliamp signal to feed a remotely located GPI.
Simple gate position indicators only showed the gate position. The gate limit was displayed on a separate dial or meter. With this arrangement, it was difficult for the operator to determine the gate position relative to the gate limit. The preferred method used by Woodward Governor and others was to use a dual pointer meter to show both signals on one dial. The black pointer on this GPI shows the actual gate position; the red pointer shows the gate limit.
Digital Gate Position Indicators
The digital upgrade for gate position indication is the Weschler Tricolor BarGraph GPI. This specialized digital bargraph meter has two signal inputs. Gate Position and Gate Limit are simultaneously displayed in the LED bar. The precise position, limit, or difference readout is shown on the 4-digit display. Two relay outputs are available to activate external alarms or initiate control actions. The trend arrow shows the last direction of gate movement. Three case sizes are offered: 4½” switchboard, 8¾” switchboard, 8″ round. One advantage of the bargraph display is the ability to vividly show if the gate position exceeds the gate limit. With the green gate position and yellow limit shown here, any overlap is indicated in red.
Frequently Asked Questions?
What position output signal is needed to drive the Weschler GPI?
The Weschler GPI can be ordered with a 0-10 V dc, 0-1 mA dc, or 4-20 mA dc input. The same range is used for both the gate position and gate limit inputs.
What does the digital display show?
The digital display is initially set to indicate gate position. The UP button on the front panel toggles the readout between gate position, limit and delta (difference).
How difficult is converting from an analog GPI to the Weschler Bargraph GPI?
The Weschler GPI is designed to simplify the upgrade from analog. The rugged metal case fits in the same switchboard panel cutout as most legacy GPIs. Plug-in connections are standard. For more secure wire attachment, optional terminal strip connectors accept spade lugs. An analog backplate with threaded studs is also available. The biggest difference with a Weschler GPI is the need for external power. Options for this are mains power from 85-264 V ac and control power from 12-250V dc.
Can the Weschler GPI drive a remote indicator?
Analog retransmit of the gate position is available for remote indication or connection to a SCADA system. The dc output ranges available for this option are 0-1 V, 1-5 V, 0-1 mA, and 4-20 mA.
Conclusion
Modern hydro governors use many schemes for generator control to optimize performance under varying conditions. A digital gate position indicator, along with a digital or bargraph power meter, gives the operator a bright, easy-to-understand status check of turbine and generator operation. The upgrade from analog to digital indication is straightforward and inexpensive.
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