Method Statement for MOTOR SOLO RUN PROCEDURE

TABLE OF CONTENTS

1.	SCOPE OF WORK	-	3
2.	REFERENCES	-	3
3.	PROCEDURE FOR MOTOR SOLO RUN	-	3
4.	HEALTH, SAFETY & ENVIRONMENT	-	15
5.	ATTACHMENTS	-	15

1      SCOPE OF WORK

This procedure covers the Motor Solo Run test for MV, LV motors.

2      REFERENCES

SATR-P-3407	LV – Motor Insulation Resistance and Functional Testing.
SATR-P-3409	MV – Motor Insulation Resistance and Functional Testing.

3      PROCEDURE FOR MOTOR SOLO RUN.

3.1      Pre-requisites for Motor’s prior to solo run test
The following procedure shall be followed for No-Load Run Test of De-coupled motor. For Directly coupled motor trial run test shall be done during commissioning phase.
3.1.1 The Motor / LCS Name Plate details shall be verified with the latest drawings revision.
3.1.2 Installation and pre alignment of motor with drive shall be completed.
3.1.3 All motors shall be pre-tested for its correct rotation before terminating the power cables.
3.1.4 Associated switchgear shall be energized
3.1.5 Lube oil system (where Bearing cooling system is in place) shall be tested and shall be fully operational in auto mode with all associated interlocks.
3.1.6 IPCS system shall be ready and configured with the vibration setting as per the vendor recommendations, where ever motors installed with vibration monitors. We should be able to print out the vibration graph from the system after the no load trial run.
3.1.7 Bearing and winding temperature sensors shall be tested and shall be in service with alarm and trip settings as per vendor documentation.
3.1.8 Motors with differential protection shall be tested and certified for protection’s correct functionality.
3.1.9 Motor protection relay shall be tested and certified.
3.1.10 The cable connection tightness at the motor Terminal box and Switchgear Panel end shall be checked.
3.1.11 The Motor earthing connection tightness shall be checked.
3.1.12 Check the Motor & Cable Insulation resistance test result are satisfactory.
3.1.13 Check the motor control & Auxiliary circuit connection as per schematic diagram.
3.1.14 Check the Motor feeder accessories functional test for ON/OFF/TRIP/
Emergency trip.
3.1.15 Check the Motor Space heater circuit if applicable.
3.1.16 Thermal detector test shall be done.          
3.1.17 A folder containing all the required/ relevant information’s shall be submitted to company to prove that all the  motor, associated sub-systems and safety systems are in place before going ahead with the no load trial run.
3.1.18 For all HV/MV motors, during the trial run, Luberef member with vibration recorder/analyzer shall be present to record the vibration reading for the future maintenance records.

3.2      CIVIL CHECK
3.2.1 Pre-alignment completed
3.2.2 Grouting completed

3.3      CHECKS PERFORM BY MECHANICAL TEAM.
3.3.1 Check the motor is decoupled from the load.
3.3.2 Check the tightness of Motor fixing arrangement.
3.3.3 Motor shaft shall rotates freely after un-coupling.
3.3.4 The lubrication and ventilation systems shall be verified.
3.3.5 Mark Magnetic centre if applicable.

3.4      INSPECTION TEST PLAN FOR ELECTRICAL WORK
During No-Load run of Motor the following parameters shall be recorded in the 
approved inspection test plan.
3.4.1 Current in each phase
3.4.2 Winding temperature for MV Motors.
3.4.3 Drive end and Non drive end bearing temperature.
3.4.4 Ambient Temperature.
3.4.5 Speed (rpm)
3.4.6 Direction of Rotation.
3.4.7 Vibration measurement (Acceptance Criteria as per 2.6 )
3.4.8 Noise measurements as applicable.

3.5      MOTOR NO-LOAD TEST

Motor no-load test shall be as follow

Motor Rating (kW)	LV Motors	MV Motors
L1 >250kW	2 hrs Trial Run	2 hrs Trial Run
≥ 55 kW ≤ 250 kW	2 hrs Trial Run	2 hrs Trial Run
< 55 kW	2 hrs Trial Run	--------------
For Pump test	Shall be check only direction of the motor	--------------
* For Directly Coupled    Motors	Trial run test shall be done during commissioning phase	--------------

3.6      MECHANICAL VIBRATION

Evaluation of the machine vibration by measurement of non-rotating parts.

At normal operating temperature, the vibration velocity shall not exceed 2.8 mm/s RMS , or 4 mm/s PEAK, in any direction.

Motor Frame Vibration Velocity: The vibration severity of the motor frame, including main terminal boxes, should not exceed 4.5 mm/s rms.

For bearing fitted with proximity probes, the unfiltered peak-to-peak value of vibration (including shaft ‘run out’) at any load between on load and full load shall not exceed the following values.

The maximum acceptable values of DE / NDE bearing temperature during Solo run shall be 54°C (Ambient) + 10°C

N° of Pole	Vibration (µm)
Two-pole motors	50µm
Four-pole motors	60µm
Fix-pole or higher motors	75µm

The following certified testing instrument shall be used for measurements :

3.6.1 Insulating tester & Multimeter

3.6.2 Digital AC/DC Clamp Meter

3.6.3 Tachometer Non contact type

3.6.4 Infrared Thermometer

3.6.5 Thermometer / Temperature Gauge

3.6.6 Vibration Monitor

3.6.7 Digital sound Level meter

Note:

In case when Vendor testing procedure using specific vendor particular test formats
are envisaged only for such special application and can only be carried after Company approval.

Note: All the meters shall be checked for valid calibration prior to measurement

3.7      NOISE LIMITS

3.7.1 Unless otherwise specified, the sound pressure level shall not exceed 85 dB in the work area, i.e., any position accessible to personal not less than 1 meter from equipment surfaces.

3.7.2 In the event that more stringent limits are required, this will be indicated in the

VENDOR’S documentation.

3.7.3 Noise level is measured by using digital sound level meter.

3.8      UTILITY OF MV MOTORS

I. Introduction

The starting of large motors and their associated loads has always presented an electrical and equipment challenge. Large motor starting can disrupt processes, affect other connected utility users, and even prevent a successful start. The trend in recent years has been an growing increase in the use of large electric motors, sometimes at very remote sites with little ability to support high-current starts.

MV AC Adjustable Speed Drive [MV ASD] technology has advanced as well. Using MV drives to accelerate large motors to speed and connecting them without power surges has become more economical. This paper outlines the motor, drive and system technical areas and tradeoffs to enable proper consideration and selection of MV ASDs for synchronized starting applications.

II. Starting Large Motors

Starting a large motor induction or synchronous motor by connecting it directly across its utility source can create large voltage disturbances.

This voltage disturbance results from the large initial current required at standstill, called “locked rotor current”. For most induction motors this starting current is about 600% of the motor’s running amperes. Figure 1 show a typical induction motor characteristic at start, including both per unit torque and current.

Notice that the line current level remains high for most of the acceleration period. Once the motor speed is past the speed where its maximum [breakdown] torques point occurs, the current falls to a running level determined by the load and the design slip.

                

                 Figure 1 Full voltage start of single or multiple induction motors

III Effects and Impact of Across the Line Motor Starting

The starting-induced voltage disturbance has several undesirable results in several areas. Consider the following:

a. Remote locations on long power lines – the overhead line utility feeds to these sites are highly reactive in their impedance characteristics. Since induction motor starting power factor is typically 0.20 lagging, voltage drop at the utility feed can be high.

b. Many new motors applications are very high power – since plant production is increasing, loads such as ID fans and mills are growing. In other industries such as petrochemical large compressors are moving from gas turbine and internal combustion prime movers to electric motors. Since many of these applications are located in remote areas or where the existing power system is at or near capacity, the voltage drop issue compounds to become especially critical.

c. Processes in rest of facility may suffer from voltage drop - any time the voltage feeding motors or plant loads falls to less than 90% of rated levels the result can be a major disruption, from disoperation to process shutdown.

d. Utility company restrictions - utility providers may either forbid or restrict high-current starts, or charge high rates for a long period following such starts. Such regulations and restrictions can come from commitments to other nearby customers to provide power at contractually guaranteed voltage levels.

Reducing Starting Current

Motor inrush current varies directly with voltage applied to the motor. To reduce system voltage disturbance, the starting current can be reduced by using one of various types of starting equipment that temporarily reduce the motor terminal voltage. Figure 2 shows such an arrangement.

          

                               Figure 2 Reduced voltage start of induction motors

Reduced voltage starters have several effects beyond current reduction. First, the torque available to start and accelerate the connected load decreases by the inverse-square of voltage. At 60% voltage, for example, available torque is 60% x 60% = 36%. While this might be sufficient for such loads as fans or pumps, a mill load requiring 100% motor torque would not start.

Second, the current and start torque keep the same shape as the motor applied at full voltage. The minimum torque [pull-up torque] also reduces with applied voltage reduction, and may not be high enough to accelerate some loads to past the critical breakdown [maximum design torque] point. Third, incoming amps are still highly reactive, so voltage drop to the motor will roughly be reduced in proportion to the reduction in starting current.

One final note is appropriate. Most synchronous motors started across the line develop torque using a cage-type rotor winding. The resulting sync motor starting current inrush characteristics are of a magnitude and shape quite similar to a squirrel cage induction motor of the same size.

IV. Some Effects Of Across the Line Starts On The Motor

Every time a motor is started across the line, it produces several areas of high stress in the motor.

1. The very high starting currents put mechanical stress on the stator windings, Such stress cycles contribute to winding fatigue that can lead to stator insulation failure.

2. The high current through the stator quickly raises the temperature of the windings. Each acceleration cycle takes some life from the motor windings insulation. The longer the cycle of acceleration, the more heat is built up in the stator. Protection is needed to prevent successive starts from causing irreparable damage to the windings. Motors are specified and designed with an allowable limit on the number of starts per hour.

3. The rotor also carries very high currents during the full voltage, high-slip acceleration cycle. The magnitude of the rotor heat is roughly equal to the amount of energy contained in the connected load at its final velocity. For very high inertia loads, such as a cement kiln ID fan, a motor that must start the fan across the line must be designed with much more mass to absorb the heat from the start. Such designs can be very expensive.

Using a reduced voltage starter does reduce stator heating, but does nothing to reduce the amount of heat induced in the rotor during a direct online start. A reduced voltage start does tend to lengthen the start cycle and could possibly allow some of the rotor heat to be dissipated during the start cycle.

However, the total amount of heat injected into the rotor for a given start is the same as if it were controlled by a full voltage starter.

V. Starting motors Using Adjustable Speed Drives [ASDs]

Slip is the difference in actual rotor speed and the synchronous speed of the motor. The synchronous speed depends on motor design and applied frequency. This relationship is shown by the formula below:

Sync RPM = 120 * frequency / number of poles

For example, a 4-pole motor run on a 60 Hz supply would have a synchronous frequency of 120 x 60/4 = 1800 rpm. At 30 Hz, the same motor’s sync RPM would be 900 RPM, and so forth.

Figure 3 shows general induction motor speed-torque characteristics, the shape of which was shown in the earlier starting current discussions.

        Figure 3 General speed torque characteristics of an induction motor at a particular

        applied frequency

                              

Referring to Figure 3, motoring torque is produced only when the motor turns at a small RPM difference below the synchronous speed. This is typically on the order of about 1% of synchronous speed.

The rated torque of the motor is the design value on the motor nameplate that is developed with rated voltage and rated frequency at the rated slip RPM below the synchronous RPM. In English units, this rated torque can be calculated as

Rated Torque in lb-ft = Rated HP x 5252 / Rated RPM

For example, for a 7500 HP 900 RPM synchronous speed and a rated speed of 892 RPM,

T rated = 7500 x 5252 / 892 = 44159 lb-ft

All the across-the-line induction motor starting characteristics discussed so far depend on the motor current and torque design starting at 100 percent slip. It has already been shown that a motor designed for 50 Hz will turn at half its rated RPM on a 30 Hz supply. The induction motor characteristic then becomes a family of curves as frequency increases from near zero, to rated speed. Figure 4 shows this family of curves.

             Figure 4 Speed torque characteristics of                                      Figure 5 Load acceleration and line amps of                                 

            an induction motor on an increasing [ASD]                                   for a Voltage Source  ASD feeding                                 

                                                                                                                   and induction motor  

Figure 4 Speed torque characteristics of an induction motor on an increasing [ASD] applied frequency During the acceleration, frequency and voltage are generally controlled such that full voltage is reached at the design rated RPM of the motor. Motor voltage and current are regulated to provide speed and torque control to the load. The voltage to frequency ratio is held roughly proportional. In practice torque developed at very low frequencies falls off and extra voltage above the value of the volts / HZ ratio is automatically applied to regain the lost torque.

An AC ASD would accelerate a constant torque load such as a conveyor or cement mill by advancing frequency as shown below in Figure 5.

Several things can be noted from the simplified drawing in Figure 5.

1. First, the motor delivers torque to the load from the part of the torque curve to the right side of the peak [breakdown] torque point, at low slip, as if it were operating at its rated running electrical conditions. This means that the stator or rotor currents are no higher than under normal operation.

Therefore there is no longer any limit on the number of starts in any time period.

2. For a VSI [Voltage Source Inverter] topology drive using DC link capacitors, the AC utility amps reflect the kW actually being delivered to the load. Figure 5 shows the relation of utility amps vs. load RPM for a VSI ASD for a constant torque load. Utility amps start out very low [transformer magnetizing amps plus initial low kW] and increase as speed and kW increase.

3 For a current source topology drive [with DC link inductors], the start cycle utility line amps are higher than for a VSI drive. In some cases, line current is roughly equal to stator current, and is approximately constant for a constant torque load. Stator amps are determined by the load torque as a ratio of rated amps and torque. Essentially, the stator amps and line amps do not exceed the actual load amps, This eliminates all the utility supply problems described above. If the utility can sustain the final loaded motor amps then it can always sustain the ASD line amps during a start.

VI. Synchronized Motor Starting Using the ASD

The preceding information provides a basis to apply the advantages of the ASD to what is called “synchronized starting”. In synchronized starting, ASDs are used to accelerate a motor and its connected load to line frequency equivalent speed and then connect them to the power grid. This synchronized starting causes little impact on utility current or voltage beyond normal running values for the motor and load.

The arrangement shown in Figure 6 is typical of a VSI ASD connected to a single motor for the purpose of synchronized starting. A review of the circuit and a synchronized start cycle follows.

Figure 6 Typical one-line of a single VSI ASD synchronized start system for an induction motor

The major components included in the system of Figure 6 are summarized below.

1. M Induction motor to be started

2. Converter-Inverter – ASD variable frequency rectifier and inverter.

3. M1 & M1A Input disconnect and pre-charge contactor

4. PT Voltage sensing transformers for input and output

5. Drive control microprocessor- based drive control with synchronizing logic

6. L-1 Output isolation inductor for closed transition of motor to utility

7. M2 Drive isolation contactor and switch – open during utility operation

8. M3 Bypass contactor controlled by drive synchronizing microprocessor

9. CTO Current sensing transformer to assure utility current flow after synchronizing.

            10. Relay 25 Independent synchronizing check relay used as verification of synchronize

      conditions.

4      HEALTH, SAFETY & ENVIRONMENT

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The entire worker shall be given a full safety induction course & HSE training on all aspects of health, safety and environment together with regular refresher courses as applicable.  All employees shall strictly follow the project health & safety rules and regulation.  The environment in and around the work area shall be well protected.

All persons involved in the Energization must wear PPE suitable for the task being undertaken by them and the same shall include the following as a minimum:

·         Helmet

·         Safety shoes

·         Safety glasses

·         Safety overalls

Inside substation shall be available:

·         Platforms & mats that are adequate suitable for that rated operating voltage)

·         Insulating gloves

·         High voltage insulating rods that are adequate suitable for that rated operating voltage

·         Fire extinguishers (CO2)

·         Safety mask

5      Attachments

Attachment 1 – SATR-P-3407 (SAUDI ARAMCO TEST REPORT)

Attachment 2 – SATR-P-3409 (SAUDI ARAMCO TEST REPORT