Below are three industrial applications which were open for bid. Sales techniques that were attempted with each application are also given. The applications demonstrate the need for a consultant to be utilized rather than maintaining a dependence upon a selling vendor.

Power Quality and Drives LLC offers consulting services. When the service is utilized, the equipment specified will be generic so that, in most cases, any manufacturer can meet the specifications. The equipment may then be purchased from the client’s normally used vendor.

Application #1

Replacement of a 250 HP, 1725 RPM wound rotor motor with a new 1750 RPM DC motor and control was required. The requirement included the use of field weakening with the new motor in order to drive the machine at 2100 RPM or higher if possible.

The maximum speed capability of the copper tube drawing machine was not known, but the maximum speed would be determined by test with the new drive.

The user had three considerations by which the new motor would be selected:

a) A constant torque application would require a 20% increase in horsepower in order to gain a 20% increase in speed. Therefore, the user would use a new motor rated at 300 HP.

b) An eighty year old, 250 HP mill motor is quite capable of developing 275 HP on a bad day. The designers of machinery were aware of the full capabilities of the mill motors and, consequently, often took advantage of the service factor which was inherent within the motors even though the service factor was never indicated on the motor nameplate. If it were indeed the case that the existing motor was required to develop horsepower in excess of 250, the user would need a 400 HP motor.

c) Meter the existing motor for current draw when the machine is operating at its maximum load. The current reading would allow an estimate of the maximum horsepower requirement at 1725 RPM. If the machine required 20% less than 250 HP, then the new motor could be rated 250 HP. If the motor was developing 250 HP or higher, then the new drive should be sized for an additional 20% horsepower. Metering is the preferred method of selection.

The sales personnel reasoned as follows:

“If I quote a 300 HP drive, the price of the project may be so high that the user may not spend any money and, therefore, I won’t make a sale.

“If I quote both a 250 HP and a 300 HP drive and try to explain to the user why he may need the higher horsepower motor, he may get confused and then buy the drive from some other distributor who doesn’t confuse him.

“Therefore, I will quote a 250 HP motor and, if he complains later that the motor can not run fast enough, I will tell him that we were asked to replace the motor and that we did so on the basis of the motor nameplate.” See Torque Capabilities of DC and AC Drives in the Constant Horsepower Range Using a Wound Rotor Motor Replacement as a Typical Application Example.

Application #2

A 2 HP variable frequency drive was powered from a 750 kVA upstream transformer. Forty feet of pipe and wire and 150 feet of bus duct were utilized. Upon application of power to the terminals, the inrush charging current caused the input devices of the drive to immediately burn out. Had an input line reactor been used as per the drive instruction manual, the drive would have been protected from the distribution system short circuit capacity. See Variable Frequency Drives: Source Impedance and Line Reactors.

The sales personnel reasoned as follows:

“I am competing against the bearing and mechanical equipment distributors who also sell drives. They are knowledgeable about mechanical devices but don’t know what a line reactor is. If I attempt to sell a reactor with the drive, my price will be higher than the other distributors who do not sell reactors and I will not make a sale.

Therefore, I will never discuss short circuit capacity with my customers and will quote only the drive which the customer has requested. If the customer later has a problem with the drive, I will send in a serviceman.”

Here is the scenario that follows:

Some manufacturers will replace a small drive under warranty if the unit fails due to a line reactor not being used. However, they do not want to see the second unit come back. The distributor knows that the drive may be replaced under warranty and therefore sells the drive without a reactor.

The serviceman visits the customer and examines the burned out drive. The customer is then advised that a reactor is needed. The service call will cost the customer $500. The reactor, which would have cost $150 if quoted for purchase with the drive, will cost $200 because, at the present time, a competitive price is not needed. The serviceman returns the next day to install both the reactor and the new drive for an additional $500 service charge.

The customer has now paid $1200 for a $150 reactor in order to protect a $400 drive. In addition, one day of production has been lost.

Application #3

It was desired to save energy by reducing the speed of a centrifugal pump on an oil filtration unit. According to the affinity curve, a 20% reduction in flow will allow a 49% reduction in energy. The affinity curve gives the performance of the pump at the points of greatest internal efficiency when pumping against zero static head. However, all pump systems will have a static head which the pump must work against. In most applications, the static head will reduce the energy savings by one-half to one-third of what the affinity curve indicates. See Elusive Energy Savings: Centrifugal Pumps and Variable Speed Drives.

In addition to the existing fifteen feet of observable vertical head, the oil filtration unit received the incoming oil and distributed it through many smaller pipes that utilized ninety degree turns along the journey to the filter. The piping presented additional head within the system.

The oil filter was changed at the beginning of each month. When new, a filter could present a typical three to fifteen pounds of head to a system, depending upon filter design. At the end of the month the head would increase significantly as the oil path became increasingly obstructed by the contaminates which accumulated in the filter. In this application, without metering motor current, an estimated energy reduction would be 15%.

The sales personnel reasoned as follows:

“I will advise the customer that the 20% reduction in speed will give a 50% savings in energy based on the affinity curve, which is the data that is used by the drive manufacturers in all applications and is accepted as a close approximation by the utility company in most applications.”

Here is the scenario that follows:

The utility gives the incentive to pay for the cost of the new drive and the customer makes a purchase. Shortly after installation, the facility personnel will discover that the payback time will be much longer than that estimated by both the vendor and accepted by the utility.

When the drive needs replacement or repairs during the next eight to ten years, the facility personnel will not have retained knowledge of why the drive was initially installed. At that time the drive will be replaced without an incentive from the utility.

Upon replacement, the maintenance personnel will be happy because the drive can be replaced quickly. The manufacturer and the selling vendor will be happy because another drive will be purchased. The utility will be happy because there will be a continued 15% energy reduction. The production manager will be happy because the equipment returned to operation. However, the low return of perhaps 4% per year or less on a ten or twenty thousand dollar drive investment is not discernible and, therefore, management does not realize that the money may have been better spent in some other area that would have increased production. It is a win-win-win-lose situation. The company loses. See Payback Analysis for Variable Frequency Drives.

It is often said that a consultant is not necessary because of the good service that is available from the vendors. The necessary question that arises is simply:

Do you want a skilled consultant sitting on your side of the table and looking out for the best interests of your company, or would you prefer the service of the above noted vendors who are sitting on the other side of the table and trying to sell what there is to sell?

For our non-American friends who visit this web page: skullduggery is “treachery” and afoot means “walking about.”