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)
HJ International Latin America, Inc.
DEFINITION
1.4
1.2
1
Load p.u.
0.8
rms equiv
0.6
0.4
Transf p.u.
0.2
22
19
16
13
10
7
4
1
0
Demand curve RMS value in kVA
Cm = ---------------------------------------------------Nominal kVA value of the transformer
HJ International Latin America, Inc.
Regarding cycles of equivalent loads
Note 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…
HJ International Latin America, Inc.
Cycles of equivalent loads
IEEE 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!!
HJ International Latin America, Inc.
Diagram of temperatures
GRALTA
GRUPO DE INVESTIGACION
EN ALTA TENSION
HJ International Latin America, Inc.
Diagram of temperatures
Direct measurement
(thermocouples)
Indirect measurement
(resistance)
Posición
vertical
ΔΘTO
ΘSUP
Nivel Superior
Aceite
ΘTO
ΔΘT
Calculated
(recomendations
IEEE)
ΔΘT
ΔΘW
ΔΘT / 2
ΔΘH
Nivel Superior
Devanado
ΘH
Punto
caliente
ΔΘAO
ΔΘW
ΘW
ΘAO
Tanque
Aceite
ΘA
Nivel Inferior
Devanado
ΘINF
ΔΘBO
GRALTA
HJ International Latin America, Inc.
GRUPO DE INVESTIGACION
EN ALTA TENSION
Temperatura [ºC]
Devanado
Regarding the limits of load and temperature
For operations above the nominal load
Per IEEE C57.91 – Table 6
DISTRIBUTION TRANSFORMERS
Top oil temperature:
120degC
Temperature of the hot spot of the conductor:
200degC
Short duration load (1/2 hour or less)
300%
HJ International Latin America, Inc.
Regarding the limits of load and temperature
For operation s above the nominal load
Per IEEE C57.91 – Table 7
POWER TRANSFORMERS
Top oil temperature:
110degC
Temperature of the hot spot of the conductor:
180degC
Short duration load (1/2 hour or less):
200%
HJ International Latin America, Inc.
How a COMPLETE heat run should be done…
HJ International Latin America, Inc.
DEFINITION:
Factor 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
HJ International Latin America, Inc.
Average loadability of distribution
transformers en the system
(Example)
•
The average sizes in the
grid can be reduced in
factors of 2 to 5!!
HJ International Latin America, Inc.
0-10%
>25%
10-25%
OPTIMUM SIZING
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.
120,000
Costo total
100,000
USD
80,000
Costo energia
60,000
40,000
Costo activos
20,000
0
15%
25%
60%
La
HJ International Latin America, Inc.
80%
110%
THE COMPROMISE…
WHERE WE ARE AT
TODAY:
Cm = 15 %
WHERE WE HAVE TO BE:
Cm = 60 to 75 %
HJ International Latin America, Inc.
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
HJ International Latin America, Inc.
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.
HJ International Latin America, Inc.
(Fuente: Redes de EEPPM)
Other variants practiced currently
• Digital measurements
• Remote readings
• Remote signals
HJ International Latin America, Inc.
(Fuente: Redes de EEPPM)
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)
HJ International Latin America, Inc.
AVERAGE LOAD
50 – 75 %
CRITICAL
LOAD
ZONE
IS EVERYTHING CLEAR ?
HJ International Latin America, Inc.
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
HJ International Latin America, Inc.
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.
HJ International Latin America, Inc.
The areas of Over-Current Protection in a
transformer...
HJ International Latin America, Inc.
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.
HJ International Latin America, Inc.
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.
HJ International Latin America, Inc.
The solution that the CSP transformer offers…
CAJA NEGRA
CONVENTIONAL
HJ International Latin America, Inc.
SELF-PROTECTED
The solution that the CSP transformer offers…
HV ARRESTER
LV ARRESTER
LV BREAKER
FUSES
HJ International Latin America, Inc.
The solution that the CSP transformer offers…
SIGNAL
LIGHT
HANDLE AND
EMERGENCY
OVERLOAD
LEVER
HJ International Latin America, Inc.
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
HJ International Latin America, Inc.
A practical application of the proposed
model
Case CFE – Veracruz District/Division
Pilot grid used to size unit with an optimum Cm
HJ International Latin America, Inc.
Summary of the pilot project achieved in the
City of Veracruz - Mexico
1. GRID
2. Number of units
3. Average kVA
4. Total KVA
5. Kwh./year
6. Fcme
7. Capitalized cost
units + losses
8. % Capitalized cost.
9. Type of units
HJ International Latin America, Inc.
INSTALLED
39
43.1
1,722.5
1,012,283
15.2%
US$65.8k
100%
Conventional
OPTIMIZED
39
16.8
655
1,012,283
39%
US$34.4k
52.2%
CSP
Summary of the pilot project achieved
in the City of Veracruz - Mexico
HJ International Latin America, Inc.
Important points for a successful
application
COORDINATION OF PROTECTIVE DEVICES AND REAL
EXERCISES OF OVERLOAD PROTECTION
T
HJ International Latin America, Inc.
R
Tk  T0   Tk
R0
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
HJ International Latin America, Inc.
kVA = X/2
The experience in Mexico was worth the
effort…
Letter from the Sub-Director of CFE indicating all the benefits
achieved.
HJ International Latin America, Inc.
Other recommendations:
The case of transformers in Distribution Substations
Primary and secondary distribution cables
NATALIA
Orlando Giraldo – Sales and Operations Manager - HJ International Latin America
orlandog@h-jenterprises.com – USA (636) 677 3421 – (Colombia) 57 1 478 4141
END
HJ International Latin America, Inc.