Product(s): |
Bentley Hammer |

Version(s): |
V8i, Connect Edition |

Area: |
Modeling |

# Problem

What is the purpose of the Efficiency field for a turbine in HAMMER?

# Solution

The turbine efficiency field allows HAMMER to compute how much of the hydraulic torque at the turbine is converted to torque at the turbine’s generator. This can then be compared to the (electrical torque) load on the generator in the load rejection case. If the torque at the generator does not match the electrical torque, then the turbine will speed up/slow down. The efficiency is assumed to be the peak or best efficiency point, which corresponds with the initial conditions flow and head.

- The turbine characteristic curve (from the selected specific speed) is only used to determine the head-flow-power relationship of the turbine.

- The efficiency is basically used to compute how much of the hydraulic torque at the turbine is converted to torque at the turbine’s generator. This is then used to determine if the turbine speeds up or down, based on the difference between the hydraulic torque and electrical torque.

- The efficiency is only used with the load rejection and instant load rejection cases, because the load acceptance and load variation cases assume that the turbine governor is always at synchronous speed.

- From the initial conditions, the hydraulic torque can be computed. The hydraulic torque times the efficiency that you enter equals the electrical torque for synchronous speed.

- For a load rejection case, you must enter a curve of electrical torque over time. If the net torque (hydraulic torque times efficiency minus electrical torque) at a particular time doesn’t equal zero (synchronous speed), the turbine will speed up or down accordingly.

- For an instant load rejection case, HAMMER assumes the initial electrical torque is at synchronous speed (hydraulic torque times efficiency) and then instantly drops to zero in the first transient simulation time step. The magnitude of this drop (in terms of electrical torque) influences the hydraulic results.

# See Also

Calculating initial electrical torque for use with the Load Rejection turbine Operating Case