Jaap E. Daalder

A new method suitable for real-time generator coherency determination

The aim of this paper is to illustrate that wide area generator speed measurements combined with Fourier analysis can be used to determine coherent generator groups. Studies are based on simulations in a 68-bus test system. Three test cases are investigated where the new method is compared to conventional methods based on the generator speed, modal analysis, and phasor angle measurement. The method introduced in this paper has proven to be an interesting alternative for generator coherency determination. It gives almost identical results to the offline methods based on the generator speed or modal analysis. Based on their trustworthiness the test cases indicate that the method reflects a more accurate coherency than the conventional online method based on phasor angle measurement. Moreover, compared with online applications using modal analysis the method supports real-time applications better according to its less extensive computational requirements.

Protection Scheme for Meshed Distribution Systems with High Penetration of Distributed Generation

This paper identifies the impact of high DG penetration on protection coordination and proposes a protection scheme to mitigate the identified problems, in a network with high penetration of DG. The scheme emphasizes on keeping most DGs on line to supply loads during the fault, without putting DG or any part of the distribution network in islanding operation, whilst ensuring that the conventional overcurrent protection devices (breakers with overcurrent relays - reclosers - fuses) do not lose their functions and their proper coordination

An adaptive scheme to prevent undesirable distance protection operation during voltage instability

An adaptive algorithm to prevent undesirable distance protection operations during voltage instability is proposed. The algorithm is based on mathematical logic blocks and uses the rate of change of voltage as an additional relay criteria to increase the relay security with respect to voltage instability. Studies are based on simulations using two different test systems: a 15-bus system developed by the authors and the Nordic32 system. The investigation shows that undesirable zone 3 distance relay operations can be the difference between a blackout and a recovering system during voltage instability. However, simulations have shown that the adaptive algorithm may save the system from a collapse. Although the algorithm prevents mal-trips due to voltage instability the reach of the distance relay will not be restricted.

Voltage Sag Source Location Methods Performance Under Symmetrical and Asymmetrical Fault Conditions

When several utilities operate interconnected power systems, a voltage sag generated in the grid of one utility may affect the loads connected to other utilities. From this point of view, it has become a crucial issue to identify the location of the source of a voltage sag. This paper describes and compares the methods for voltage sag source location. The methods are applied to locate the source of voltage sags considering symmetrical and asymmetrical faults. Radial and meshed areas are also analyzed. The results show that the available methods are not totally reliable and more research is needed to extend the location methods to meshed systems

Real time optimal interruptible tariff mechanism incorporating utility-customer interactions

An optimal power flow based framework is proposed to determine the incentive rates of an interruptible tariff mechanism (ITM) on an hour-to-hour basis. Interaction between the utility and customers contracting interruptible load is incorporated in the analytical framework by formulating customer response functions to the ITM. It is shown that ITM is able to reduce costs and aid in system operation during peak load periods. The IEEE 30-Bus system, considerably modified to represent different customer characteristics, has been used for the study.

Avoiding voltage collapse by fast active power rescheduling

Abstract Basic ideas for a method where the active power production is rescheduled in an automatic (fast) way to increase the loadability of the power system during a voltage instability are presented. Active power production is a parameter that is controllable during this instability phase and it may have a positive influence on the system vulnerability to collapse, especially when current limitations of the generators are involved. Depending on the strength of the system, two major objectives can be distinguished: to strengthen a local area from collapsing or to avoid an increase of the voltage depressed area.

A new protection scheme to prevent mal-trips due to power swings

New distance protection algorithms based on mathematical logic blocks are introduced in this paper. The algorithms prevent mal-trips due to power oscillations using additional criteria in combination with traditional distance relaying. These additional criteria are based on symmetrical components and the derivative of the phase angle associated with the current as seen by the relay. A simulation is performed in an eighteen bus system developed by the authors where the performance of the algorithms is analysed. No timer settings as is necessary for conventional power swing detectors are needed. Thus different cycle times of the power oscillations will not affect the performance of the algorithms. Neither does an area in the RX-diagram have to be pre-defined which may cause extraordinary difficulties for applications serving long distance transmission lines.

Distance protection and voltage stability

In this paper the influence of zone 3 distance relays in the case of voltage instability is examined. Different types of relay characteristics are analysed. An adaptive algorithm to prevent undesirable zone 3 operations during voltage instability is proposed. Studies are based on simulations in a fifteen bus system developed by the authors. Data on the mixture of electromechanical, solid-state and numerical distance relays in the Swedish transmission system are presented together with statistics of zone 3 operations from the start of year 1985 until the end of 1998. The investigation shows that undesirable zone 3 distance relay operations during voltage instability can be the difference between a total blackout and a recovering system. Simulations have shown that the adaptive algorithm may save the system from a collapse.

Continuum gradient-based shape optimization of conducting shields for power frequency magnetic field mitigation

A shape optimization technique for quasistatic field problems has been developed. The optimization is based on computing the continuum sensitivity function by solving an adjoint problem. We show how this technique can be used to compute, in a very efficient way, the optimal shape of a conducting (or ferromagnetic) shielding structure, in order to minimize the magnetic field in the region of interest. A two-dimensional example of shielding three-phase underground cables is considered

Operation of Distributed Generation in Weak Grids with Local Critical Load

The integration of distributed generation (DG) in weak grids can help the utility in providing reliable power to critical and sensitive loads. That requires the modification of the DG controller to be able to continuously supply power to the loads that are connected at the same bus. In this paper, an algorithm has been developed to ensure the continuous and proper operation of a DG either in case of grid power existence or grid outage. In normal operation, the DG is capable of supplying power into the grid and maintaining the nominal voltage. Moreover, the DG controller, in case of grid failure, is capable of maintaining the nominal values of both the voltage and the frequency. The transients due to the transition between the two modes are discussed