Developing automated Hardware-In-the-Loop tests with RTDS for ...

Developing Automated Hardware-In-the-Loop Tests with RTDS for Verifying the Protective Relay Performance l l2 R. Iracheta-Cortez , , N. Flores-Guzman l Management of Industrial Mathematics , Center for Research in Mathematics (CIMAT), Guanajuato, GTO, 36240, Mexico Catedras Conacyt2, University of Istmo, Tehuantepec, Oax, 70760, Mexico [email protected], [email protected]

Abstract- This paper describes the steps for carrying out automated Hardware-In-the-Loop tests to protective relays with the real-time power system simulator RTDS. The main features with such tests are the performance verification of new protective relays,

before

their

commissioning

within

the

electrical

substations, and the improvement of the power system reliability.

A brief description of the software, hardware and applications of

the RTDS simulator is made. A digital simulation model of a power network is proposed, as a benchmark case, to perform the

Hardware-In-the-Loop tests with the distance relay SEL-421. Finally, a report is made to analyze the performance of the distance relay.

Keywords- Real-Time Simulator; Protective Relay; Hardware­ In-the-Loop tests; Power Network, RTDS;

I. INTRODUCTION Real-time simulators are powerful tools for the analysis, design, control, protection and operation of power systems. The evolution of these simulators over the last decades is the result of many research and development efforts. For instance, Transient Network Analyzers (TNA's) or analog simulators evolved into hybrid simulators when appeared the first digital simulation tools, for analyzing power systems, such as the Electromagnetic Transient Program (EMTP) [1-3]. Then, the fully digital simulators appeared with development of digital processors. Hybrid simulators peaked from the 70's and up to the 90's. The foundation of these real-time simulators is the combination of TNA's with the digital solution of an EMTP­ type program [4-5]. One of the first applications for these simulators was used to program the transmission line equations in DSPs while the rest of the power network was simulated with TNA's. During the 90's appeared the first fully real-time digital simulators which are based on technology of supercomputers. With these simulators, larger power networks can be simulated fully digital and in real-time for analyzing electromagnetic transients and also, for carrying out Hardware-In-the-Loop (HIL) tests to electrical devices, mainly, in protection and control systems [6-11]. The Real­ Time Digital Simulator (RTDS) was the first of its kind The authors gratefully acknowledge support from the National Council on Science and Technology (CONACYT) and the Center for Research in Mathematics (CIMAT).

worldwide for being used in power system applications. It was developed by the Center of Research in HVDC of Manitoba in Winnipeg, Canada. Subsequently, the Electrical Research Institute of the Hydro-Quebec power utility developed HYPERSIM simulator. The common characteristic between RTDS and HYPERSIM is that both simulators use the nodal EMTP solution [6, 12]. During the 90's, the high-tech company OPAL-RT Technologies developed the eMEGAsim simulator. This simulator is a little bit different to the previous two due to its solution is based on a state-space representation of the power network in Simulink®. The main requirement to perform real-time simulations with eMEGAsim is to build the model of a power network and its controls in Matlab/Simulink®. Fig 1 show the real-time simulators RTDS, eMEGAsim and HYPERSIM A common characteristic of these power real-time digital simulators is its parallel processing capacity for simulating electromagnetic transients in large networks [14-17]. In addition, its design allows a wide range variety of tests in electrical equipment such as digital protective relays and control systems. This article describes a procedure to develop automated Hardware-In-the-Loop tests to a distance protection relay with the RTDS simulator. These tests are used in this paper to verify quickly the performance of new protective relays, before their cOmmissIOning within electrical substations, for improving the reliability of the power system.

a) b) c) Fig. I: Real-Time Simulators: a) RTDS,b) eMEGAsim and c) HYPERSIM.

II.

SOITWARE AND HARDWARE

The RTDS simulator is a supercomputer with software and hardware specially designed for the simulation and analysis of electromagnetic transients in the electric power systems. The RTDS hardware is based on a parallel processing architecture customized to simulate with one or several processors the general solution of the power network. The addition of more processors permits to simulate large power networks without affecting the real time simulation capacity. Additionally, the RTDS software counts on a wide library of power components, control and automated protection systems; those together with a very friendly user interface that make the assembly and study of a wide variety of electric AC, DC systems easier and integrated. Because the operation of real time of the RTDS simulator is achieved on an indefinite and sustained way, tests to electric equipment are no longer exclusively reserved for analog simulators [5, 9]. A. RTDS Hardware

The RTDS simulator is organized in hardware units, named racks, they are mainly made up of processing and communication cards as seen in Fig. 2. Each rack is designed to include from 2 to 6 PB5 processing cards and 1 communication card with the working station (GTWIF, Giga Transceiver Workstation Interface Card). All cards inserted in the rack are connected to a common plate located in the back part of the simulator. Additionally, the modular design of RTDS simulator permits the addition of multiple racks and the addition of cards of analogic and digital signals. The main types of cards used with the RTDS hardware are following described: The PB5 is used to solve equations representing the power system and the components of the control system. The minimum performance of operation of an RTDS rack is achieved with 2 PB5 cards. Each rack permits the nodal solution of 1 or 2 electric sub nets up to a maximum of 90 single phase nodes or 30 three phase buses per subnetwork. The integration steps (�t) used in the real time simulation can be adjustable from 10 to 50 us. The rest of the processors of the rack are required to solve individual power components (transmission lines, generators, transformers, etc.) and its controls. The main function of the GTWIF card is the handling of communication between the RTDS simulator and the guest computer. This card does not participate actively in the solution of the power system but play an important role as an interface device and simulation control. The specific functions of this card are: a) load, start and stop simulation cases, b) Generation of timers, c) synchronization among racks, d) Racks diagnostics, e) All communication with the RSCAD® software.

Backplane Fig. 2: Hardware arquitecture RTDS®.

B. RTDS Software

The RSCAD® Software is the graphical interface that allows users to build, compile, execute and analyze simulation cases. This software uses the algorithm developed by H. Dommel to get the digital solution of electromagnetic transients of an electric power network modeled with constant or distributed parameters. The essence of the Dommel algorithm consists on representing any element from the power system as an equivalent Norton type into the discrete time domain. To get such as equivalent, integration numeric methods are used to discretize the branch current equations described in the continuous time domain, for each of the elements integrating the power system. With the branch equations in the discrete time domain are obtained relations among voltages and currents to the present time (t) and past time (t-�t). To start the simulation it is important to specify the fixed step of integration (�t), and additionally, the initial conditions of the system to update the states of the simulation in t �t, 2�t, 3�t, ... up to the maximum time of the simulation tmax.. In Table I are shown the discrete equivalents for the basic elements of the power system: resistance, inductor, capacitor and transmission line. The general solution outlined by H. Dommel to calculate the transitory electromagnetic in any power network configuration is given by =

[G] [ ( t ) ] [ i ( t ) ] - [ hist (t - �t ) ] v

=

(la )

where G is the matrix of nodal conductance of the electric net, v(t) is the vector of nodal voltages for time t, i(t) is the vector of current sources for time t, hist(t-�t) is the vector of historical of currents of the system for time (t-�t) [1]. The conductance matrix G of the power network is kept constant when a fixed step of time �t is used and there is no switching of circuit breakers. The construction of G follows the same construction rules of the matrix of nodal admittance during in steady state analysis.

Com onent Resistance: R

a)

Table I: Discrete Equivalents EMTP Solution

III. MAIN ApPICATlONS OF RTDS SIMULATOR

Inductor: L

b)

rY'\rV\

ikm

+ � , , , L-ok

m

()

d· vkm t = L� dt

2L

RL=-,GL=l/RL

Ilt

ibn (t) GL Vbn (t)+ histL (t-Ilt) =

histL (t-Ilt) = 20LVon (t)+ histL (t-2�) c)

Capacitor

C

.

�� + kI � dVkm ikm ( t ) = L dt

RC =

Ilt 2C

,Gc =11 RC

ikm (t) Gc Vkm (t)+ histc (t-Ilt) =

histe (t-"'t)=-20eVkm (t)-histe (t- 2"'t) LosslessTransmissio

d) n Line

TL

i ..

k0 •

i .. III 0 m

I

_

aVkm ax 8ikm

_

i(x,t)

=

_

ax =

�

L C

i"", (t) = (1 / Zm) V k (t)+ histbn (t-,)

at '

- vt

x - vt -

.1._

Zc = ,)L/C,r=//v=/075

at ' OVkm

(x ) +f, (x + ) ( ) Zef, ( + )

v( x, t)= Zef,

:�r:.r+ fl?�� -.1.

aikm

vt ,

x

vt

The main applications of RTDS simulator are summarized in Fig. 3. From this figure, one can say that Hardware-In-the­ Loop tests; to digital protective relays and control systems, and Power-Hardware-In-the-Loop tests; to distributed generator, electric vehicles batteries, motors and loads, are exclusively of real-time simulators such as RTDS [18]. This is because such tests allow the simultaneous interaction of the digital simulation with the physical equipment. Additionally, with the RTDS simulator, open and closed loop tests can be implemented for both; individual protection relays and full protective relays schemes. In these tests they may include equipment compatible with lEe 61850. Fig. 4 shows a schematic drawing of the manner how closed-loop testing protective relays is performed. Hardware-In-the-Loop tests are useful: 1) To assess the performance of individual protection relays, protection schemes and control systems before commissioning, 2) Know the answer of the power system to different failure scenarios, 3) to improve the safety and reliability of protection systems and control and 4) Testing new ideas and concepts for the development of new protection relays and/or control systems. Other applications with RTDS simulator can be used to perform many studies and analysis of smart grid applications, distributed generation and advanced power electronics.

in" (t) = (II Zmh (t)+ histmk (t-,)

hist""' (t- r)=-(1 / Ze)vm (t- r)-i... (t- r) histmk(t-r)=-(I / Zc)v.(t-r)-ibn(t-r)

Wide Area Protection and Controllesting Distributed Generation (Renewables)

1=======1

=

(lb)

Sub-index A denotes a set of nodes with known voltage while sub-index B denotes a set of nodes with unknown voltages. The latter nodes needs to be calculated at each time step by solving

VB ( ) [GBBr {iB(t)-histB(t-�t)+GBAVA(t)} (Ie) GBB GBA• t

Education and Training

Power Electronics

Equation (la) can be splited as follows

�t)] t his ] ) ] ) [iA(t [ [VA(t A(t GAB] [GAA GBA GBB vB(t) iB(t) histB(t-�t)

LargeScale Real­ �:::Tim = = e=S=im=ulat = =io=ns= �

-..

Smart Grid Development and PHILSimulation Testing

�

HIL ControlSystems Testing

Protective Relay Testing with IEC 61850

Fig. 3: Main applications of the Real-Time Digital Simulator (RTDS).

=

This equations are equivalent to solve a set of linear equations at each time-step with constant sub-matrices and This happens as long as the time-step remains unchanged during the entire simulation time. The history terms, at the right side of this equation, have also be updated at each simulation time-step. For running efficient simulations of electromagnetic transients in power systems, it is highly recommended to calculate only at one time sub-matrices and before entering to the recursive loop of time. Additionally, the power network solution can be parallelized due to conductance matrices are usually sparse.

GBA

GBB

Digital Simulator RTDS

Equivalent (THI)

Thevenin Equivalent (TH2)

Fig. 4: Hardware-In-the-Loop tests to protective relays.

IV. ELECTRICAL NETWORK MODEL IN RTDS Fig. 5a shows the unifilar power network diagram used for testing the distance relay. The system is made up of two Thevenin equivalents of 230 kV rms at 60 Hz. The corresponding data of source impedances are provided in Table I. Both Thevenin equivalents are connected by means of a transmission line of 100 km. Its geometric configuration is illustrated in Fig. 6b. This power network model have switches between each Thevenin equivalent and the transmission line. In addition, it has also placed a fault module at the middle of the transmission line to cause different types of contingencies for the real-time simulation in RunTime. The fault control is designed to select the type of fault, its position and its resistance. The geometric data of the transmission lines are captured in the T-Line/RSCAD module to generate the parameter file *.t1b. Additionally, the T-Line module is configured for this line as Bergeron and also, transposition and interpolation options are enabled. Table II provides the information of positive sequence impedance (ZI) and zero sequence impedance (Zo) of the transmission line. These impedances can be obtained from file * .tlb. The complete design for this power network in Draft and RunTime modules is illustrated in Appendix A. Tabla [. Thevenin Equivalent Data THI TH2 Source R-RiL R-RiL Source Type Vnom (kV) 230 230 28.943