Sunday, September 18, 2016

Plant Design: Motor Protection Parameters

The table below is an example of a working protection parameters of an electrical system. A parameter sheet such as this will enable the designer to tabulate necessary initial values and  calculations.

NO.
Equipment name
Nominal power
(kW)
Circuit calculation current(A)
CT trans. ratio
Zero sequence CT trans. ratio
Circuit type
1
Motor Pump No.1
3400
355.6
1000/1
2000/1(Differential)
100/1
Vacuum breaker
2
Motor Pump No.3
1400
146.4
500/1
100/1
 Vacuum breaker
3
Motor Pump No.3
1000
104.6
400/1
100/1
Vacuum breaker
4
Motor Pump No.4
400
41.8
200/1
100/1
F-C circuit
5
Motor Pump No.5
900
94.1
300/1
100/1
F-C circuit
6
Motor Pump No.6
710
74.3
200/1
100/1
F-C circuit

First is to work out in calculating the circuit current of a three phase motor circuit:

Circuit Current=kW/(√3∗kV∗pf )

Instrument and protection CTs are governed by standard IEC 60044-1 . The matching of CTs with protection relays calls for a thorough knowledge of CTs. The following section gives a few reminders in determining   the CT ratio, the table below will give the recommended primary CT ratio for various circuit current in the  motor protection  section. See (link) for complete list of CT ratio per application.

CT Primary=kW/(√3∗kV∗pf *η )


If you do not know exact values for ϕ and η as a first approximation, you can assume that: cos ϕ = 0.8 ; η = 0.8. T. The secondary circuits of a CT must be suitable for the constraints related to its application for  or protection purposes.

CT Secondary  
For use in a local situation Isn = 5 A
For use in a remote situation Isn = 1 A

The use of 5 A in a remote situation increase the cross section of the line or the sizes of the transformer (lost in line). IEEE C57.13 Table 8 - Standard multi-ratio current transformer taps gives the standard ratings for instrument transformers. Sequence CT Ratio are constant 100/1 in 4.160 and 6.9kV Circuit.

For the circuit Type in 6.9kV , there are two recommended circuit types. Use  Vacuum Circuit when the Current reached above 100 Amps or Fused Contractor when dealing with currents below 100 Amps.

Sunday, September 4, 2016

Power System Study for CADPI

Our freelancer have been involved in the Analysis of Electrical System of Central Azucarera De Don Pedro (CADPI) in Nasugbu , Batangas Philippines. The scope of the projects includes Short Circuit Analysis, Load Flow and Protective Device Coordination evaluation of the Plant.

Electrical Design Projects in USA

Our freelancer have handled major electrical design projects for clients in USA. Among these projects are design contracts under MR Engineering Consultants:


1. RECOVERY CAFE-FIRST CHRISTIAN CHURCH
80 South 5th Street, San Jose CA 95112

2.HOTEL CLARIANA-5 Storey Commercial Building
100 East Sta. Clara, & 10S 3rd St.  San jose CA. 95113

3.North Bascom- Medical Office
105 North Bascom Ave. #100 & 101 San Jose CA

4. Elite Educational Institution
155 Anza St. Fremont CA

5. St. Martin of Tours
200 O' Conner Dr. San Jose CA

Electrical Design for ME Sikat Construction Corporation

Our engineer has undergone Electrical Design of Transmission Line for a temporary facility for ME Sikat Construction Corporation. The project also includes Electrical and Plumbing Design for Ground Floor and Mezzanine of Quezon Hall U.P Diliman Campus and Asian Institute of Tech Vldg UP AIT Diliman, U.P Diliman Campus.


Additional Projects:
1. Electrical Design of Transmission line project Temporary Facility.


(Finished 1.11.17) 

Electrical redesign for Cement Manufacturer Association of the Philippines

Our Freelancer worked on the Electrical redesign of the building of Cement Manufacturer Association of the Philippines. The design works includes the details for installation of the grounding system and rewiring of  tapping to Genset. The project was successfully closed on July 2016.


Saturday, September 3, 2016

Power System Study of 3x135 MW CFB Thermal Power Plant FDCMPC

Our freelancer has undertaken Power System Study for 3x135 MW CFB Thermal Power Plant of FDCMPC in Cagayan De Oro, Misamis Oriental in the Philippines. The scope of the project are Load Flow, Short Circuit Analysis and Motor Starting Analysis.



Monday, June 13, 2016

Generator excitation control operation

Increasing the output voltage of a generator is achieved by adjusting the magnitude of the excitation current. This happens because as DC current is increased, the rotating magnetic field increases thereby increasing the generator  voltage induced in the stator conductor.     As the voltage is increased, the generator will transfer more MVAR into the power system.
Instead of collector rings, suppose that a  brushless generator above  is used in our example. The exciter is provided from the DC winding which is wound in the stator. The rotor produces ac current that is feed into the rectifier built in the shaft. The rectifier converts AC to  DC and feed the rotor windings.

To control of the rectifier  output in the field windings of the excitation generator, voltage regulator receives its command signal from the AC voltage controller which monitors the ac voltage of the monitor.


The limitation of the generator due to current in the stator should follow within the machine capability curve. Increasing the excitation current of the generator to deliver MVAR will produce heating in rotor winding. alternatively, if the excitation is reduced voltage and VARS will fall. then the machine will have weak magnetic field .

Technical Data for Generator 60WX18Z-090 with Static Excitation 158,8 MVA 13800 V 60 Hz p.f. = 0,85 Tcg = 33 °C Temp.-Cl. = 130(B
In the capability curve, the horizontal axis is the  reactive power in per unit quantity, where 1 pu =159 MVAR and the vertical axis is the active power per unit quantity.