New vision regarding the real average load of distribution transformers in Latinamerican electrical grids. The situation and the various paths to a soluction. Arguments based on IEEE C57.91-1995 (R2004)

1
New vision regarding the real average load of
distribution transformers in Latinamerican
electrical grids.The situation and the various
paths to a soluction.Arguments based on IEEE
C57.91-1995 (R2004)
2
DEFINITION
Demand curve RMS value in kVA Cm
--------------------------------------------------
-- Nominal kVA value of the
transformer
3
Regarding cycles of equivalent loadsNote that
the levels of overload and its duration are
extracted from the proper curves of the real
load and not from a standard!!
The accummulative concept of the loss of life
day, month, year, all its life
4
Cycles of equivalent loadsIEEE C57.91-1995
A transformer subjected to any one of these 3
cycles will exhibit the same performance in terms
of energy
While the RMS value of the load curve is below
the nominal capacity of the transformer, the loss
of life of the unit will be below the maximum
permitted!!
5
Diagram of temperatures
6
Diagram of temperatures
Direct measurement (thermocouples) Indirect
measurement (resistance) Calculated (recomendatio
ns IEEE)
7
Regarding the limits of load and temperatureFor
operations above the nominal loadPer IEEE C57.91
Table 6DISTRIBUTION TRANSFORMERS
Top oil temperature
120degC
Temperature of the hot spot of the conductor
200degC
Short duration load (1/2 hour or less)
300
8
Regarding the limits of load and temperatureFor
operation s above the nominal load Per IEEE
C57.91 Table 7POWER TRANSFORMERS
Top oil temperature
110degC
Temperature of the hot spot of the conductor
180degC
Short duration load (1/2 hour or less)
200
9
How a COMPLETE heat run should be done
10
DEFINITIONFactor regarding energerized medium
load

• Annual invoicing in GWh
• Fcme -----------------------------
  ---------------------
• CITD fp 24 360
• CITD Installed capacity of Distribution
  Transformers, GVA
• fp Global power factor of the system

11
Average loadability of distribution transformers
en the system (Example)

• The average sizes in the grid can be reduced
  in factors of 2 to 5!!

12
For the losses and typically kVA cost that we
found throughout the Latinamerican grids, the
minimum operative cost for Cm to be between 50
and 75 of the nominal capacity of the
distribution transformers.
OPTIMUM SIZING
13
THE COMPROMISE
WHERE WE ARE AT TODAY
Cm 15
WHERE WE HAVE TO BE
Cm 60 to 75
14
Determination of the real demand
Indirect measurements CEMIG (Gemini)
Compare the energy sold to the end users
connected to the transformer to the energy the
transformer has the capacity to deliver
The real losses at the sight of installation are
not accounted for.
Administration of actives due to accummulated
loss of life
15
Direct measurement of energy delivered by the
transformer

• The reading is compared to the energy sold to the
  end-users connected to the unit.
• If you compare the energy delivered by the
  transformer to a load profile, you will have a
  precise vision of the percentage of load.
• (Fuente Redes de EEPPM)

16
Other variants practiced currently

• Digital measurements
• Remote readings
• Remote signals
• (Fuente Redes de EEPPM)

17
Distribution of loads in a grid with optimum
sizing

• CRITICAL ZONE WITH THE NEED TO ADEQUATE THERMO
  PROTECTION
• Example Cm/Fd (0.60/0.65 0.92)

18

• IS EVERYTHING CLEAR ?

19
Factors to consider for the optimum sizing based
on the consumption of energy

• REAL LOAD CURVE OR CHARACTERIZED AND 2 EQUIVALENT
  CYCLES.
• DETERMINE THE RMS VALUE OF THE LOAD CURVE BASED
  ON THE ACTUAL CONSUMPTION.
• LIMIT THE PROJECTION OF THE LOAD CURVE TO NO MORE
  THAN 5 YEARS.
• DEFINED A UNTI SIZE THAT WILL REACH ITS OPTIMUM
  LOAD IN THE PROJECTED TIME.
• SELECT AN APPROPRIATE THERMAL PROTECTION

20
The type of transformer to be used in an
optimized load environment
To successfully operate distribution transformers
at Cm levels between 50 and 75, it is
considered imperative that the protective devices
used for the transformer, identify those levels
of overload in magnitud and duration that cause
loss of life above the maximum permitted.
21
The areas of Over-Current Protection in a
transformer...
22
The type of transformer to be utilized on optimum
load environments and
THE DEFINITIONS OF THE PROTECTION TO BE UTILIZED

• Emphasis on the control of the thermal
  compartment (following the load currents
  and the interior temperatures)

• Asset management of the grid

• Reduction of installation costs.

• Significant reductions of the global failure
  indices of transformers in the distribution
  system.

23
The type of transformer to be utilized in an
optimum load environment
Lighted signal or Information sent remotely
Priviledging the need to interrupt dangerous load
y even finding a better solution, we are
installing CSP type transformers to provide an
exact thermal protection and the capacity to
interrupt at the site.
24
The solution that the CSP transformer offers
CAJA NEGRA
SELF-PROTECTED
CONVENTIONAL
25
The solution that the CSP transformer offers
HV ARRESTER
LV ARRESTER
LV BREAKER
FUSES
26
The solution that the CSP transformer offers
SIGNAL LIGHT
HANDLE AND EMERGENCY OVERLOAD LEVER
27
The signal lamp as an element in providing an
effective managemente of loads and assets along
with an important role in balancing loads.

• LIGHT OFF

• STATUS OF GRID AND LOAD ARE NORMAL

• LIGHT ON

• STATUS OF GRID AND LOAD ARE ABNORMAL

28
A practical application of the proposed model
Case CFE Veracruz District/Division Pilot grid
used to size unit with an optimum Cm
29
Summary of the pilot project achieved in the City
of Veracruz - Mexico
1. GRID INSTALLED
OPTIMIZED 2. Number of units 39
39 3. Average kVA
43.1 16.8 4. Total KVA 1,722.5 655 5.
Kwh./year 1,012,283 1,012,283 6. Fcme
15.2 39 7. Capitalized cost
US65.8k US34.4k units losses 8.
Capitalized cost. 100 52.2 9. Type of
units Conventional CSP
30
Summary of the pilot project achieved in the City
of Veracruz - Mexico
31
Important points for a successful application
COORDINATION OF PROTECTIVE DEVICES AND REAL
EXERCISES OF OVERLOAD PROTECTION
32
When making an economic evaluation of a project
using conventional vs CSP type transformers
THE SIZE OF TRANSFORMER BEING COMPARED ARE
DIFFERENT
CONVENTIONAL
kVA X
kVA X/2
33
The experience in Mexico was worth the effort
Letter from the Sub-Director of CFE indicating
all the benefits achieved.
34
END
Other recommendations
The case of transformers in Distribution
Substations
Primary and secondary distribution cables
NATALIA
Orlando Giraldo Sales and Operations Manager -
HJ International Latin Americaorlandog_at_h-jenterpr
ises.com USA [phone] (Colombia) 57 1
478 4141