Annual rate of increment

I am working in Coal India Limited. There are two grades of employees, i.e. Executives (Officers) and Non-Executives (Staff). The wage period of Executives is for 10 years (1st January 2007 to 31st December 2016) & for Non-Executives it is for 5 Years (1st July 2011 to 30th June 2016). Till 22nd November 2011, I was working in Non-Executive Grade having (1) Basic Pay of Rs. 30,000/-, (2) Variable Dearness Allowance @ 0.7% of Basic Pay i.e. Rs. 210/- (which is revised quarterly), (3) Special Dearness Allowance (it remains fixed) @ 1.795% of Basic Pay i.e. Rs. 538.50p & (4) Attendance Bonus @ 10% of the Basic Pay i.e. Rs.3000/-, totaling to Rs. 33748.50p. All the above four heads are known as Wage Components. On my above post the rate of Annual Increment was 3% of my Basic Pay which comes to Rs. 900/-. In November 2011, I was promoted to Executive Grade and joined on 23rd November 2011. As per formula adopted by CIL for fixation of Basic Pay in Executive Grade on promotion from Non-Executive grade (Sum of Wage Component + one increment on last Basic Pay in Non-Executive Grade to be divided by 100 + %ge of DA in Executive Grade and hence the resultant be multiplied by 100 for fixation of Basic Pay and remaining %ge to be treated as DA in Executive Grade) and accordingly my Basic Pay on promotion to Executive Grade became Rs.22800/- and since the Dearness Allowance was 52% at that time the amount of DA became Rs.11856/-. On my promoted post the rate of Annual Increment was 3% of the present Basic Pay i.e. Rs.684/- Under the above circumstances, though I have been promoted the amount of my Basic Pay & Annual Increment has reduced. Since HRA is paid @ 20% of Basic Pay it also reduced. I would be obliged if you could reply me whether Basic Pay, rate of Annual Increment can be reduced on promotion.