Real network demonstrations

At the fourth step of the development process, real distribution network demonstrations are conducted. At this stage, problems that may arise in real network implementations are identified. Practical issues such as the need for additional measurements or the adequacy of measuring accuracy of existing equipment are discovered and the operation of the real

SCADA Measurements from

the power system

Commands from coordinated voltage control On-line controls

and monitoring

OPC

RTDS rack PC running

RSCAD PC used for

network management

RSCAD Shared

files

Matlab used for data transfer

OPC

Matlab

State estimation

Coordinated voltage control Emulates real distribution network

Could also be implemented as a part of DMS

implementation of the developed control algorithm is verified also in the real distribution network. The delays of data transfer are realistic and their effect on the operation of the algorithm can be evaluated.

The back-up procedures for situations where an important communication channel or some controllable component fails should also be tested at this development step. The voltage control algorithm should be able to detect these situations and to function reasonably also when the input data is inadequate or when some controllable component is unavailable for control. In these situations, one alternative is to use a set of predetermined control values that are such that all node voltages remain above the feeder voltage lower limit in all loading and generation situations. If the voltage rises excessively at some generator node, the unit is disconnected by its overvoltage relay.

At the beginning of real distribution network demonstrations, the algorithm is usually used in an open-loop configuration where the inputs of the algorithm are taken from the real distribution network but where the control algorithm does not yet directly control the network equipment. After successful open-loop operation is confirmed, closed-loop tests can begin.

Only a few real distribution network demonstrations have been reported in publications.

[103]-[105] describe the real distribution network demonstrations of GenAVC system that implements coordinated control of substation voltage through control of AVC relay set point.

The GenAVC is implemented as a separate controller and includes a state estimator and a CVC algorithm based on [44]. In [103] the open-loop operation of GenAVC is tested in two trial locations. In [104] and [105] the closed-loop tests are reported.

[71] reports the progress of field trials in project DG DemoNet. Field trials are conducted in two network locations and substation voltage and reactive powers of DGs are used as control variables in the demonstrations. The control of DG real power is not included although proposed in previous publications of the same project [69]. The CVC algorithm is implemented as a standalone C++ application and communicates with the distribution network through a real SCADA (Siemens SICAM 230). COM interface is used between the CVC algorithm and the SCADA. Critical distribution network nodes are determined by simulations and voltage measurements are installed to these critical nodes. State estimation is not used. In reactive power control, a contribution matrix is utilized. Hence, if the network switching state changes, the reactive power control algorithm might not operate correctly as the critical nodes change and the contribution matrix needs to be redetermined. The DG DemoNet voltage control strategy is planned to remain in real distribution network use also after the trial phase as [71] states that a number of DG projects have been approved for connection to one of the trial networks only on the condition that they participate in the DG DemoNet voltage control.

In [40] an algorithm utilizing optimization to determine tap positions of substation main transformer and step voltage regulators on feeders is tested in a real Japanese distribution network. The realization of the demonstration is not thoroughly documented.

Real distribution network demonstrations are planned also in Italy [54], in the UK [61] and in France [106], [107] but publications reporting the results of these demonstrations have not yet been published.

A real distribution network demonstration of one CVC algorithm is documented in [P4]. The Matlab implementation of [P3] is used to realize the CVC algorithm and data exchange with SCADA is realized using OPC. In the demonstration, the CVC algorithm operates only as an advisory tool. Measurement data is transferred automatically from SCADA to the CVC algorithm but the control commands given by the CVC algorithm are approved and executed by the network operator manually. Input data of the CVC algorithm is obtained using state estimation. The arrangement used in the demonstration is represented in Figure 4.12. [P4]

Figure 4.12. The arrangement in the real distribution network demonstration.

In the demonstration, the CVC algorithm and the state estimator were implemented as a Matlab program and run on an additional computer added to the control room. The CVC algorithm is, however, designed so that implementing it as a part of the already existing DMS would be quite easy. The DMS already includes a state estimator and, hence, only the CVC algorithm would need to be implemented. Moreover, the DMS network model is always at

SCADA DMS

Measurements from the power system

Commands from coordinated voltage control

PC used for coordinated

voltage control PC used for network

management Matlab OPC

State estimation

Coordinated voltage control

Operator

AVR

AVC relay

Substation Heinäaho

Feeder Kihniö Feeder Ritari

Setting values

Soininkoski hydro power plant

PC used for coordinated voltage control PC used for

network management Feeders Äijänneva, Kurjenkylä and Autio

the same switching state as the real network and, hence, the algorithm implemented as a part of the DMS will be able to operate also in unusual network switching states. If the algorithm is implemented as a separate controller, the network model is static and the network data and switching state need to be maintained in two places (NIS database and the CVC controller) or some kind of automatic data exchange needs to be set up.