After installation and commissioning, all the functions as per individual elements and their interconnected wiring is required to be checked under cold test, i.e., without energisation of any element in the panel or at the machine. After cold test, individual elements and independent test shall be conducted under energised condition.
After this limited interconnected elements shall be checked for its signal exchange and functioning. All inputs and outputs shall be monitored at PLC Input Cards. Similarly, isolating the PLC output terminal Opto card which is an interface between PLC output and actual elements shall be tested. At this stage all the drive parameters shall be uploaded through PC or display keyboard at individual drive. AEF shall be checked for its functioning and DC bus generation as the input supply to the all drives. A simulation test without running the machine is conducted for software program responsible for overall run of the machine. After successful test, whole machine along with Panel are ready for Trial Run.
System Testing
Cold test
For check of wiring and interconnection among various elements is to be ensured cautiously with respect to design documents. A separate folder for ‘terminal board’ drawing has been made with cross reference and with no place for amguity. The results are recorded in form of tabulated check list:
Earthing test
Total impedance including cables from any unit point to earthing pit must be below 0.3Ω.
Energisation of PLC for Input Signal test
Before proceeding, measurement of cold condition resistance between positive (+ve) and negative (-ve) points at all TERMINAL boards is measured & recorded as a Ohmic reference value, to declare healthy conditions.
Measurement of Encoder waveform
With slight rotation of encoder, under flexible coupled condition; the wave of signal A and B with corresponding inverted form are measured at source and receiving end for no loss & deformation of true square wave. In our case, 128 pulses are recorded for every quarter of motion.
Analog signal drop
Accuracy in drive synchronisation is significant. Few mV signals were issued from the source and a record at receiving end was measured. Variation at both ends was recorded. One sample exercise given and it was repeated for next 11 analog signals. It confirms the selection and usage of screened analog cable is in order.
PLC supply energisation
With prompt alertness, all cage PLCs are energised step by step. Checking, for PLC inputs by actual operation of mechanical dogs, stoppers, levers, limit switches, proximity sensors, push buttons, thermostats and pressure switches etc., is done with actual machine operating conditions.
Simulation for PLC output devices
Isolating PLC output card/connectors, an external power source with short circuit protection is applied to all PLC triggered output devices. On actuation, its applied effect on indicators, solenoids is recorded for all output signals.
Test for PLC interface Opto-cards
Disconnect PLC output terminal board cum connectors; and a 24V DC signal (protected by 250 mA) is injected to input of Opto-cards and corresponding output should operate a control relay or an LED indicator at cage station, control desk or a signal transmission to corresponding receiver end at respective terminal board. The exercise is to be repeated for 31×8=248 times as per drawing and each record is to be kept separately.
Test for emergency P.B. pressings
This is very important to ensure the effect of EMG. P.B. is positive, especially when there are 12 locations of emergences. EMG. Signal is processed directly by hard wired logic & via PLC, in such a way that even if a wire is opened, the action should be taken as if emergency exists. The record is made & checked in a preventive maintenance schedule.
Active energy front energisation
Keeping all MCB in off conditions, only 3 phase supply is given to external charging circuit and DC bus is energised and a watch on DC bus voltage is kept. Simultaneously inbuilt fan in LCL filter must be in rotation; else stop charging and connections / fuse etc. are to be checked. The procedure is followed as per the following sequence flow diagram.
Cage panel testing
3 phase & 415V supply is measured before main’s isolating switch. Impedance of R, Y, B line with respect to connected motors should be recorded as reference for healthy condition for motor. The variation must be controlled, by adjusting carbon brush angle and shape. The carbon brush must be under spring pressure. All the carbon bushes & slip ring connection must be clean and tight in an enclosed chamber.
Take up panel testing
On 3 phase supply energization, start procedure as per following sequence.
Software Loading
PLC software is developed as per machine and should be uploaded in all PLC units and HMI touch panel including developed screen pages, data and windows Xp. Drive Wizard and Parameter uploading is required to be done in all Drives.
Active Energy Front Device parameters are loaded for control and performance of DC bus voltage and by bidirectional flow of energy during inversion and conversion processes.
Software simulation without running of machine
The Input and Output functions for all cages are checked as per PLC I/O list. Following three inputs from main panels to AEF units are to be checked by simulation and its output logics should be noted.
• Request for synchronies with main utility networks (Regeneration).
• Shut down DC bus.
• Run enables/disables for base and block of IGBT.
Simulation of digital signals (I/O) at main panels
All signals coming from cages to main PLC and command signal from main PLC to cages are simulated for their functions as defined in I/O list. For reference following strings are given.
• Readiness of all cages and Start/stop of all cages.
• Warming when conductor present length target is reached.
• Start/stop of hydraulic pump motor is simulated, especially when line is not running. It is exclusively simulated when any of cage station is selected for same activity.
• Load in progress in all cages.
• Issue of load clearance on station selection request.
• Over all fault signal creation.
Simulation of message/alarm at Touch panel HMI
All cage faults i.e., by opening left/right guard, Wire break, Pintle opening, Loading arm is not at home, Station select, Drive trap, Panel over heat, No application data entered, Encoders cables faults, Encoders rotation is not getting sensed, Motor over heat, Indexing gear is engaged, Load clearance from main control desk can be displayed in HMI.
Among PC, main PLC (Programmable Logic Controller), HMI (Human Machine Integration), cage 12, 18, 24, 30 and all the 7 drive units. Further Ethernet communication by RJ-45 connection among all units as covered above.
Auto tunning of drives
Mechanically all motors including all cage, capstan, take-up, auto traverse and motor are un-coupled from machine before proceeding for online tuning.
The actual cable under application is included as a part of motor winding resistance. After entry of motor name plate data like kW, RPM, power factor, supply voltage, number of pole.
Encoder data like pulse per revolution (PPR), gear ratio, direction and alarming conditions are entered as parameter in the drive manual.
The run command is given for auto-tunning and motor winding data, losses at no load, slip, etc., are internally calculated and kept in the drive memory.
Conclusion
The article discussed various initial checks and examining healthy conditions of all sub-assemblies of main equipments. A cold test check is conducted without energising the equipments for all its inter-connections at terminal boards.
DC bus is especially checked for polarities by feeding say 2V cell. Earth resistance test for both power and screen cable is conducted for satisfying minimum value criteria.
A record of tests is tabulated as reference values at beginning. Low signals like encoder and analog signals are measured for proper reference and mV drop, if any.
AEF panel, take-up panel and other cage panels are energized following their sequence as per flow chart. Software in PLC is uploaded including operating system, and machine. A simulation test without run is conducted for software check.
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Great article. Connecting cables are an expensive progression and need to be treated with the utmost care. And throughout the time between cable installation and termination, cables are prone to damage from a variety of issues including foot traffic and the movement of building resources.