The Energy Transition’s Impact on the Accumulated Average Efficiency of Large Hydrogenerators

Abstract

<div><div><div><p>The energy transition is aimed to take advantage of the operational flexibility of hydropower to extend the in- tegration of intermittent renewable sources. Consequently, the hydrogenerators will have to operate in regimes far away from their designed best-point operation. In order to accurately assess the impact, this paper presents a useful approach to determine the overall operating efficiency of synchronous generators under intermittent operation. An accumulated average efficiency (AAE) model is proposed and compared against an alternative approach; the weighted average efficiency (WAE) model. It is found that the WAE approach produces unrealistic low efficiencies when the generator operates in synchronous condenser mode (SCM) for long periods. In general, the AAE supersedes the WAE for all the different load distributions that were investigated. This was further illustrated by a worked example and by constructing more complex load distributions. A load distribution dominated by SCM yields a difference as high as 33.18%, while an even distribution deviates 1.43 % in their respective efficiencies. Finally, a yearly on-site measurement of our studied 103MVA generator’s concentrated load distribution revealed a discrepancy of 0.67 %, which is a significant deviation considering what the operating regime would mean in terms of economic implications.</p></div></div></div>

Loss Modeling of Large Hydrogenerators for Cost Estimation of Reactive Power Services and Identification of Optimal Operation

“…The air gap line and the OCC are found using [20] and the OCC data for G1-G4 are given in the standard datasheets of these real-world generators. Already, G2 and G3 are provided in [13] and [21], respectively. The estimated OCC profiles for G1-G4 are compared against the recordings in Fig.…”

Loss Modeling of Large Hydrogenerators for Cost Estimation of Reactive Power Services and Identification of Optimal Operation

“…A price must be paid in terms of reduced efficiency resulting from the active and reactive power provided intermittently. To quantify the impact of intermittent operation, an accumulated average efficiency (AAE) model was recently proposed to improve the accuracy in the determination of the power losses [13]. It was proposed as an alternative to the mainstreamed weighted average efficiency (WAE) model [14]- [16].…”

“…The variables in the loss separation model is I a , I f , and U a , where I * a , I * f , and U * a refer to their nominal values. The armature current is calculated in per unit as I a = √ P 2 + Q 2 /U a , while the field current is found from I f = f (E g , E p ) using the armature reaction parameters of the machine (R a , X d , X q , and X p in Table II) and the open-circuit saturation curve [13].…”

“…11. Impact of the AAE efficiency for a yearly dataset of Åbjøra hydropower plant for an increasing number of weighted zones, using the AAE method developed in [13].…”

“…Fig.1. Case study for a 103 MVA hydropower generator[13]. (a): Measured losses (P l ) for 7 different load points versus predicted loss contours using eq.…”