Design & Installation of Control & Monitoring Systems in Electrical Engineering
Design, Installation, Testing & Commissioning of Control & Monitoring Systems
Design Implementation
The preparation of the design of control and monitoring systems requires the definition of a set of actions:
- Definition of equipments and systems to be controlled and monitored (all equipments – circuit breakers, instrument transformers, isolators, switches, etc. – must be identified by a code, defined by the Construction Owner or by the designer, if no instructions exist.
- Definition of the type of control and monitoring to implement, according to the complexity of the installation.
- Definition of protections units to use, establishing the tripping matrix.
- Definition of the “set-points” of the protection units.
- Definition of interlocking matrix.
- Definition of operation sequences and sequential automatisms, if any.
- Synchronization of MV, HV and EHV (MV: Medium Voltage; 1 kV < V < 60 kV. HV: High Voltage; 60 kV ≤ V < 150 kV. EHV: Extra High Voltage; V ≥ 150 kV) circuit breakers (closing in the condition “live bar – live line”).
- Reclosing programme.
- Definition of digital and analogue input and output signals .
- Definition of general alarms and respective data treatment.
- Definition of electric parameters to be monitored and measured.
- Definition of time delays to be established.
- Definition of disturbances to be recorded.
- Establishment of switching programmes, under normal and emergency situations.
- Definition of operation sequences and sequential automatisms, if any.
- Load shedding, if required.
- Interactions between equipments and/or systems (local and remote).
- Events and respective data to be remotely transmitted.
- Control and monitoring input signal from the remote control center(s).
- General communication networks.
Documents to be Produced
Apart from single line diagrams of the global installation, showing all equipments and their codes and the protection units, it must be produced for each part of the installation and for each equipment to be controlled and monitored, the control and monitoring schematic diagrams, which are important pieces for maintenance and failures detection.
In these diagrams it must be represented all equipments to be controlled and monitored and control equipments, either manual or automatic (auxiliary relays, control switches, etc.), dully codified, interlocking (if any), as well as auxiliary contacts of protection units, pilot lights and metering equipment.
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The above referred diagrams must be complemented by wiring diagrams of power and/or control switchgears, panels and cabinets, showing the respective terminal blocks, dully identified, with the connection of conductors of internal wiring and control cables. Each conductor must be identified with a label, defining the connection in accordance with was defined in the design documents.
A cable list must also be produced, showing:
- Type of cable, number of conductors and cross section.
- Cable origin and destination.
- Cable identification, according to was defined in the design documents.
- Cable routing.
Logic Diagrams & Operation Equations
Within the design of control and monitoring systems it must also be considered the programming instructions for microprocessed units of the system, which must include interlocking, tripping orders, equipment blocking situations and eventual sequential automatisms.
These instructions may be produced under as logic diagrams or operation equations.
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a) Logic diagrams
Logic diagrams associated events (represented by capital letters) that traduce the conditions to be fulfilled to logic bloks of mathematic logical operations – logical conjunction (˄) and logical disjunction (˅).
It is assumed that an event A can have the following values:
- A = 1 – event verified.
- A = 0 – event not verified.
b) Operation equations
Operation equations use Boolean Algebra, establishing equations between the events (represented by capital letters), mathematic logical operations – logical conjunction (˄) and logical disjunction (˅) – to algebraic operations ( x ; + ).
For an event X it is assumed the following convention:
- X – event verified.
- X̅ – event not verified
Related article: Programmable Logic Controllers (PLC) for Industrial Control
Interlocking & Local Manual Control
In order to avoid wrong maneuvers that can damage the equipment and cause hazards to the employees an interlocking program must be implemented.
The most common wrong maneuvers in electrical installations are:
- Open or close isolators with the circuit breakers closed (on load manoeuvre).
- Close earthing switches with circuit breakers and/or isolators closed and with voltage present.
- Close circuit breakers and/or isolators with earthing switches closed.
- Close other circuit breakers when the protection relay 50BF is activated.
There are two types of interlocking: electrical and mechanical.
Electrical interlocking is intended to prevent non authorized electrical control and is performed through “hardware” (relays and cabling), through “software”, or a combination of both.
Mechanical interlocking is intended to prevent local manual control and can be achieved by padlocks and locks, or can be built-on, which is the case of isolators with earthing switches in substations.
Equipments can be provided with both electrical and mechanical interlocking.
Local manual control is performed close to the equipments. By safety reasons, this type of control, with the exception of emergency situations, is only possible to do when it is authorized by the person in charge of the operation of the electrical installation, which will get it “free” to be performed by a designated operator.
For manual control interlocking can only be superseded by personnel dully authorized:
“Hardware” interlocking: using control switches with key, which is only accessible to authorized personnel.
“Software” interlocking: using a “key word” that allows to supersede interlocking only to authorized personnel.
Also read: Electric Stress Control in Cable, Joints & Terminations
Installation, Testing & Commissioning of Control & Monitoring Systems
Control and communication cables may be installed in concrete trenches in the switch yards or in cable trays inside technical buildings. Optical fiber cables in the switchyard are usually installed in the bottom of concrete trenches, inside high density polyethylene.
These cables must be segregated from power cables to avoid electromagnetic interferences and protected from heat sources, like steam lines.
All conductors of multicore cables must be identified with suitable labels , which content must be defined during design stage.
Splicing, joining and termination of twisted pair cables and optical fiber cables require trained, specialized and certified personnel.
When equipment arrives to site a preliminary inspection must be carried out, taking into account the following:
- A visual check up is required to verify if damage to the equipment has occurred during transportation.
- It must be assured that the main technical characteristics of the equipment meet the approved specifications.
- It must be assured that erection instructions accompany the equipment.
- It must be assured that the result of Factory Acceptance Tests (FAT) accompany the equipment.
Control and monitoring systems and equipments are installed indoors in switch gears, control cabinets and control and protection and panels and desks, apart from local control cabinets of HV and EHV (HV: High Voltage; 60 kV ≤ V < 150 kV. EHV: Extra High Voltage; V ≥ 150 kV) installed in the switch yards of substations or industrial outdoors process equipments.
In power stations, substations and industrial plants these equipments must be installed in control and/or electric rooms provided with a suitable HVAC (heating, ventilation and air conditioning) systems to control the temperature, which is recommend being not higher than 25 ºC, and the relative humidity, according to the recommendations of the manufacturers; the quality of the air must be suitable for the equipments, free of dust.
A particular care must be taken with the IP degree of protection provided by enclosures of control cabinets, panels and desks (requirement must more critical for equipments installed outdoors) and the filters of HVAC equipment must be periodically cleaned or replaced.
It shall be noted that in many countries that is not usual to install HVAC systems in public MV/LV substations (MV: Medium Voltage; 1 kV < V < 60 kV. LV: Low Voltage; V ≤ 1 kV), although it is necessary to assure a proper natural ventilation of the substation electric rooms.
Control and monitoring equipments and protection relays must be subjected to tests after manufacturing (Factory Acceptance Tests – FAT), to verify the compliance of cables with standards and regulations, and after installation (On-site or Site Acceptance Tests – SAT).
American standard ANSI/NETA (ANSI: American National Standards Institute. NETA: InterNational Electrical Testing Association) ATS-2009 (Standard for Acceptance Testing Specifications for Electrical Power Equipments and Systems), identify all inspection and test procedures for these equipments and systems.
Tests and inspections are classified into “visual and mechanical inspection” and “electric tests”.
Within visual and mechanical inspections it will be emphasized:
- Verify that FAT tests certificates and instruction manuals accompany the equipment.
- Compare equipment nameplate data, characteristics and software revision (only for micro processed equipments) with drawings and specifications.
- Verify the unit has no physical damage and that is clean.
- Check tightness of connections.
In what concerns electric tests they must be produced according to the type of equipment, and it must be performed:
- Insulation-resistance test on each circuit-to-frame.
- Checking that cable and internal connections are in accordance with the last issue of design drawings.
- Functional operation test (mainly actuation value and time delay).
- For micro processed equipments check operation of all active digital inputs, all output contacts and check all internal logic functions used in the protection scheme
After the equipment is initially energized, measure magnitude and phase angle of all inputs and compare to expected values
Tests must be carried out using proper test equipment, such as:
- Multi meters
- Clamp meters
- Voltage testers
- Relay and meter test equipment
- Insulation testers (MEGGER)
Frequency of maintenance shall be established taking into account equipment reliability requirements and the manufacturers’ manuals and recommendations.
Maintenance activities may be planned for each segment of the installation at different periods, but major industries usually once or twice a year have a global shut-down for maintenance purposes.
NETA standard MTS-2007 Appendix B recommends the frequency of maintenance tests for Electrical Power Distribution Equipment and Systems.
Maintenance activities (visual and mechanical inspection; electrical tests; tests values) for each piece of equipment are defined under NETA standard ATS-2009.
Some maintenance activities deserve a special highlight:
- Verification of the integrity of safety and tripping circuits.
- Cleaning of switchgears, cabinets, panels and desks, in order to avoid that dust causes a decrease in the insulation.
- Verification of the strength of fastening of bolts and nuts of conductors to avoid excessive heating.
- Checking of HVAC system functioning and filters.
